Need a better idea ?

[gofastsandman]

What about a bow rail holder where it starts going fore.

[McGillicuddy]

3/4" square bars of aluminum or stainless (could use tubing if you prefer); cut the ends at appropriate angles weld on 3/16" flange plates w/countersunk mounting holes and screw in place. Give bar a little quarter round to match the soft curves of the 21 and your done...