[ic] Easy way to handle a "buy over $XXX, get this free gift"

[Carlc Internet Services]

I've got a cart running interchange 5.0.1. It's been very stable
and runs great. The owner would like to do a "Buy $50 [or some
set number], get this free shirt". The t-shirt would be a sku
number in the cart (including a set number, so it might be a 
first 100 people get t-shirt sku #XXXXX for free). The other trick
would be to allow the t-shirt to select size, color, etc, like
a normal shirt from the catalog.

Any help or where I missed how to do this in the docs would be
very helpful.

Thanks in advance!
Carl
CarlC Internet Services
http://www.carlc.com/