It's been done, of course.
Four and a half years ago, in an (as always) different
context, I wrote about magnetic poetry. Magnetic poetry uses a refrigerator door
rather than an envelope, but the process is essentially the same - organize the
words so that they make sense to you (actually, "write a poem", but
that's pretty much the same thing). There used to be many online examples of this,
but few seem to still be around. There is, however, an
interesting collaborative version available online.
Go to: Are there limits to disorganization?, or
Go to: Please organize me.