Assuming the gilder is not a very new competition type, it will probably be impossible to fit a radio and a transponder (using current tec). The weight of the batteries to power such a set up for a typical soaring flight would put the thing over its max weight. It was in recognition of this that the CAA started the LAST transponder design. The same is true of some PFA and Micro types; with the very real possibility of aircraft being grounded if the original CAA mode s proposal had gone through.
Rod1