I've sent this off to nite_man, but I thought i'd mention it here too:
Basically, in src/Orbiter/OrbiterRenderer.php, look around line 1235, you'll notice a reference to DESIGNOBJ_objExitController2_CONST. This is the Exit Orbiter button, and it is hidden by default in Designer. Interestingly enough, they decided to take care of it in the global renderer class, and set the hide/unhide to unhide if the orbiter is the WIN32 orbiter. I have extended this to add the exit button to the Maemo orbiter, as such:
Add the following lines after the #ifdef block
//also NOT hidden on Maemo orbiter
if(pObj->m_iBaseObjectID == DESIGNOBJ_objExitController2_CONST)
pObj->m_bHidden = false;
recompile and use.