The Cobra's housing is convertible... the grey cap comes off of the top and allows the compass to be added there, and I think there's another module that allows the compass to be mounted to the back.
The bad news is, you will have to buy the compass housing complete. You cannot take the compass out of the wrist mount and put it into the console mount... in part because the mounts are not sold separately.
Cheapest way to go would be to find someone with a console-mount who wants to go wrist-mount and trade with them.
Leisurepro wants $50 for the console mount and $60 for the wrist unit. This is the top-mount module so you can see the compass and the Cobra at the same time.
http://www.leisurepro.com/Catalog.aspx?op=ItemDisplay&ProductID=SQTCBCC