You know that is a great question, and I have mentioned this (not on every occasion). It almost always gets the "Umm maybe that will be an option but we can't guarantee it". This always screams to me "Yeah this ain't gonna happen". Ha.
You have to prove yourself in that period. If they're hooked they will let you do anything. Also of course you have to be lucky to find open-minded managers.
In my experience if they see that you are a valuable resource management accepts A LOT.
btw, contact me, i've got some Ruby/Rails projects/work every now and then. kmc16sq@tempalias.com