for now it looks like you've got two options then.
the long, but more likely to succeed route. step out of your comfort zone and try to get yourself closer to this person. talk to them,hang out,etc.
*if you guys have friends in common use/ask them to help you get closer.*
and option two...
just do it. get yourself hyped and go tell them you like them better as a crossdresser than a woman.
it'll most likely backfire or not have an effect at all. but the human brain works in mysterious ways.
he'll have an idea of how someone else might feel about his decisions. or even better, might now see you as someone who finds him appealing(which hopefully will be a good thing.)
option 1 is tried and true. but as a completely random stranger you probably shouldn't trust i'd say go with option 2 ;)
jokes aside there's still stuff that needs to be known.
do they have a bf/so right now? are you interested in them sexually or just want them to continue crossdressing? do they CD in public or is it a private thing they've shared with you or is it something someone told/ you found out?