Does anyone know a workaround to get SLES12 to work with remote X-Servers that don't have the COMPOSITE extension?

We're using Netsarang's XManager (which works really well) and gnome-session refuses to start, because it doesn't find this extension.

This is probably also the reason why Xrdp is broken in SLES12.
Unfortunately, SLES12 ships _only_ GDM (xdm doesn't count) and Gnome3 as a full DE.

I know there are workarounds for situations where the GLX ext is missing (which gnome3 also requires), but I didn't find a lot wrt COMPOSITE.

Does anyone know?

The last resort would probably ripping out GDM/Gnome3 and completely replacing it with some other DE, though I would prefer to stay as "supported" as possible.