You have my sympathy. When I have encountered such environments/situations in the past I have referred to them as adminstrative fascism as a nod to the venerable Know your System Administrator by Stephan Zielinski.
If your target box has no compiler and you have no suitable cross-compilation available elsewhere then any non-PP module such as XML::LibXML is going to prove tricky at the very least. PP modules should still be feasible even if it is a bind installing and deleting them over and over, not that I am a user of such a PP XML module. Hopefully the reward of your work is worth the drudgery.