I was tempted to do the same thing because I am wasteful (waistful, lol
) and impulsive, and definitely have zero patience.
But, I decided not to buy it for the PS3 because I wouldn't play it enough to justify the purchase and the PS3 is in the main room with my HDMI 360 (I have 2 360s because one got RROD and got fixed, and I had no patience to wait for it, lol (I wanted the HDMI 360 anyway)).
I would just wait for it unless you really think you will play the PS3 version a lot (depends on how long your son is getting inpatient rehab, usually quickly barring complications). If when he comes home, he is going to hog up the 360, I would go ahead and get the PS3 version too.