No licence is required to fly a glider so there is nothing to transfer. Under EASA, sailplanes are in a different Category of aircraft so they are no more transferable to an aeroplane licence than heliccopter differences.
The only area where there may be some commonality, is if you have a TMG rating on a Sailplane licence and a TMG on an Aeroplane licence, then any differences on the TMG should apply to both and one could argue then apply to a valid SEP on the same licence, as experience gained in either class is countable.
FCL.710 Class and type ratings — variants (a) In order to extend his/her privileges to another variant of aircraft within one class or type rating, the pilot shall undertake differences or familiarisation training.
(b) If the variant has not been flown within a period of 2 years following the differences training, further differences training or a proficiency check in that variant shall be required to maintain the privileges, except for types or variants within the single-engine piston and TMG class ratings.
The glider is not in the same Class or Category!