Firstly, you may need to force GoMobile to run before XThreads, because, by default, it's possible that XThreads executes its code first, then GoMobile jumps in and changes the theme.
Edit the priority of the
global_start hook in GoMobile or XThreads, for example, you may open gomobile.php, find:
and replace with
which forces GoMobile to load before XThreads.
As for forced themes, that's a bit difficult. I haven't tried, but you may be able to get somewhere by fiddling around with $forum['overridestyle'] and $forum['style'] and checking for those.