Not having XTR, I can't say for sure...
It sounds like you're referring to 'slope soaring,' an altogether different problem than using thermals. I have little doubt that XTR can do thermals... I seem to recall thermal activitiy being an option when I was playing with it at the store.
But seeing how XTR goes about rendering its 'world', I doubt it. RealFlight left that cheap hack behind years ago... putting a panoramic graphic around the 'pilot', with only the aircraft (and its shadow) being a rendered/simulated part of the environment.
That's not to say that slope soaring couldn't be done using this trick; but if you're simulating slope soaring (of which the terrain is an integral part), you've got to actually have the terrain/wind interactions in the flight model.
And if you do that, you might as well render the terrain (graphically) while you're at it... and since XTR doesn't
render terrain, but rather simply provides the illusion of terrain existing...
I doubt it.
And I don't mean to make this sound like some holy war... but I do know that G3 supports slope soaring just fine. (This was actually one of the reasons I chose G3 over XTR)
The last thing I want in a heli is a few loose screws.