On Tayloring a Blouse

I am now the trepedatious owner of a dress-maker's dummy.
It's... okay.
Easier to work with than trying to pin a shirt while I'm wearing it, I will give it that much. But I have to pad the waist out a bit in order to get it to be me-sized. (The tits are fine in their lowest setting, and the hips have been appropriately adjusted, but the waist is a problem).

I've got a purple blouse on it, now, which I've pinned (for the second time) to the point of fitting reasonably.

My question is: How do you make (or taylor) a blouse so that (a) it fits when your arms are at your sides, but (b) allows you to raise your arms without pulling the whole damn blouse with you?
Help?
Suggestions?
This thing where I can't (elegantly) get things off of high shelves without having to adjust my clothing significantly is... irritating. I want full range of motion, dammit! :-P

Sleaveless blouses and knit shrugs. That's the way to go. :-P