welcome to "commuting". here you have to be part Marine. adapt and overcome.

bike shops sell expensive adapter kits that may cost 1/2 as much as the darn rack. "P" clips or clamps can be used to attache almost any thing on a bike. they are in the hardware store in drawers that have the weird stuff. the hardware store also sells very thin steel bars that can be cut at home quickly with a hack saw and then drill whatever holes you need. I like working with thin steel bars. one needs a vise, clamps, hacksaw, locking vise grips, sledge hammer and good drill bits, etc. but you can pretty much make whatever you need. hardware store also sells thin aluminum bars that can be cut, bent and drilled. but steel is real.

go forth and conquer :-)