Stretch vinyl before glueing?

I've read a lot of posts that say to heat and stretch your vinyl in order for it to conform to your fiberglass box or panel, but do you need to have it completely stretched to shape before applying spray adhesive or contact cement?  That seems to be the only way that makes sense to me, since you only want to let the adhesive dry until it is tacky and heating would probably only speed up the drying process.  I have many compound curves to conform to, so I will need to do quite a bit of stretching.  Anybody have some advice?

Also, is there any way to shrink vinyl?