thp,
im awfully sorry for that splurg i read the comments and said what I thought before your video had loaded.

I agree with ism that scaling as it stands is too fiddly and not preconfigured, maybe when you create a new item you fill the free space available?

Are you redrawing the sketch each time you adjust, or are you scaling a bitmap?

I hope its a sketch because you can get tremendous performance boost by filtering the points and removing duplicates or straight runs.
You gain an additional performance boost when shrinking them by only drawing some points (instead of every 1, draw every 2 or 3 or 4 and so on).

For obvious reasons I do enjoy sketching programs.