Here's Sharon Schamber's method of basting (Part 1 of 2):
http://www.youtube.com/watch?v=bhwNylePFAA
You don't need the footprint of the entire quilt in order to baste it.
If that doesn't work for you (or you don't have enough room to do it), then onto Plan B:
As the top is already together, the usual Quilt As You Go methods won't really work here.
So you could next try the "Divide and Conquer" method (also the book title).
Marti Michel (
http://www.frommarti.com/QIS.shtml) also recently did a book on this technique, where you quilt in sections - I think it could work for hand quilting as well.
More info on both can easily be found via a Google search.