Blocking Lace

I've been reading all of these posts on Ravelry about how important it is to block lace, and how it really makes the pattern what it is supposed to be. Which leads me to a few dilemmas. First, I'm making this Easy Lace Stashbuster Scarf out of brushed acrylic. I know that acrylic doesn't really "block" but I don't know if this would be any different. So I don't know if it would work at all. I should just do a swatch and try to block it, but the lana polo that I'm using does not rip well at all -- it becomes tangled in itself and I just have to throw it away. I know that if I do that, I would wind up throwing away the swatch because there would be nothing else that could be done with it. Second, if it does work, I have no idea how long to make the scarf pre-blocking. I have trouble determining how long a scarf should be to begin with, before you throw this blocking stuff into the mix. Someday, when I can afford nice, natural fibers, I'll be better able to predict stuff like this.