Composite configurations. The DSC Book covers them. Essentially, each admin gets their own config, which is exposed as a resource. A master, "composite" config, sucks them all in and produces the final MOF.
There's no "conflict resolution." If both sub-configs mess with the same bit, then whichever one is references last in the MOF will usually "win," but it'll cause poorer performance as the LCM will be switching back and forth, since both "conflicting" configs will be in the MOF. You need to manage that – it's a process question, not a technical one.
But the ultimate answers is one MOF per node. There's no workaround – it's that way by design.