I spoke to one of the developers of Telepathy about this, and here is what he said:
Currently Telepathy does not support this type of feature. For example, users cannot send emoticons that they have drawn themselves. Therefore, you would need to write a library for this. If you are willing to write a library, they would be happy to have this feature.
Secondly, they recommend that you write a seperate app for this feature, but use the Empathy contact list. They recommend that the feature be accessed through the accessibility menu.
Lastly, if you would like to discuss this, please contact the developers on the mailing list:
telepathy lists freedesktop org.
I hope that this is helpful. Please let me know if you have any questions, and if you do begin work on this, I will be happy to be of assistance if I can
Sincerely,
Meg Ford