You can certainly do this more dynamically (i.e. not tediously changing it frame by frame), but the method depends on what you want. An increase based on current frame position, an increase based on time independent of frames/movement? Based on screen position? All of these and any combination can be accomplished with a little math and none of them require killing yourself doing it by hand.
Incidentally, drawmethod does not require 0-256 anymore (I'm not even sure if you can use 0-256, and don't care enough to find out). It's now a base 1 decimal. IOW 1 = 100% (Normal size), 0.5 = 50% (Half size), 1.5 = 150% and so on. This makes working up the math for dynamic zooming a lot simpler.
What is the specific effect you are going for?
DC