Side Select control not available on USRP2 Source block in GRC

Hi

I am using Gnu Radio Companion on a USRP2 with a daughterboard that has
dual sides. One is only Rx and the otherone is able to be switched
between Tx/Rx. I want to be able to select between the sides but the
USRP2 Source and the USRP2 Sink blocks (unlike the USRP versions of the
blocks) do not have a side select control. Please let me know how to do
that.

Regards
Awais