Since I've got Widget on my mind at the moment (not to mention that stupidly catchy music) I'll list the improvements I made over your movie, as well as some of the things I learned about the game in the process. Hopefully it will help you out.
http://www.rphaven.org/cad/Widget2.fcm
Frame 327: You mentioned that zipping is only useful when the room is 1 screen wide, and this isn't entirely true. Since Zipping doesn't scroll the screen, and it replaces you at the center of the screen when you're done, zipping is useful any time that Widget starts on the left side of the screen. If you zip to the center of the screen and then stop, you'll be placed at the center of the screen. Note that Zipping immediately would have caused a crash here, that's why I jumped.
Frame 1532: Not sure what happened here with you. You paused to dodge the bird, I didn't have to. Many times it's possible to kill the enemies faster with some clever shooting instead of having to dodge them or take damage from them.
Frame 1770: The warp glitch in action. I tried doing some cheat searches to discover the true behavior of the L+R glitch, but I didn't find what I was looking for. As far as I can tell, Zipping will replace your current surroundings with the clipping information of somewhere up and to the right.
Frame 1880: You can jump while zipping.
Frame 1950: Since I got to the ledge faster, the ghost didn't have to knock me back down.
Frame 2046: Because the two ghosts are still on the screen, neither of the slugs appeared.
Frame 2288: I don't know what made you think it's faster to zip ahead, get hit, warp back, and walk through the enemy. If you must take damage, it's faster to just walk into the enemy and turn your back to it at the last possible moment. This causes about 2 frames of delay, whereas zipping ahead causes several frames of delay - I mean, the actual zipping forward part wastes your time.
Frame 2936: Warp glitch again. I snagged the E-tank in the box at the top of the screen. I don't know if this is useful or not, but if you're going to be taking more damage to save time throughout the movie, having more energy will allow you to do it more often. Also, note how I jumped before I activated the glitch. If you don't jump, you'll get shifted backward and stuck in the floor and it will cause several more frames of delay.
Frame 3070: Using some smaller jumps, I was able to avoid hitting my head against the wall like you did.
Frame 3265: This room was full of crash zones. My theory is that using L+R at certain points will warp you to places with invalid clipping data (off the screen or something like that) and cause the freeze. However, I was still able to zip for 5 frames here before a crash occurred.
Frame 3291: This is a really awesome maneuver. I fall to the spikes (zipping any more in this zone will cause a crash), Turn backwards at the last moment possible causing it to knock me onto the pillar, zip off the pillar, through the bird and the wall, and drop straight to the ladder. This is similar to what you did, but...
Frame 3551: Whoa, I'm still invincible! I guess climbing on a ladder preserves your invincibility after getting hurt, and changing rooms may reset it as well. I use it to walk right through the slug, shooting it a few times to knock it out of my way just as the invincibility wears off. With this head start, I use some tricky jumps to jump past all the hamburgers without even bothering with them.
Frame 3900: Zipped to the center of the screen again.
Frame 4545: No pausing, no hesitation. I only lost 2 frames of conveyor belt time because of the bee, but that's a lot less than you lost.
Frame 4661: Small jump straight onto the next platform.
Frame 4860: Another E-tank.
Frame 5036: I begin zipping toward the exit, grabbing the health refill along the way.
Frame 5150: Boss time. I had to refrain from zipping for a few frames due to crash zones.
Frame 5165: I use the time spent waiting for the shot to hit the boss to situate myself on the invisible platform. When it connects, I start blasting away. Notice how I also snag the magic expansion along the way.
And those are all the improvements I made. I think this movie might still be improvable, due to the following facts:
-I completely forgot that you can shoot with an upward slant by holding Up. I could have saved myself from taking damage a few more times with this, and I could have killed the boss a little bit faster.
-It's probably very worth it to grab the gun upgrade in the 3rd room.
That's all I have for now. Hope I helped.
