What you want cannot be done to my knowledge. Even if there were two local cores with different names and service macros, I do not think that they can share the same data at the same time, basically access arguments.
If they shared one at a time, always one not running, it still shouldn't cause constant resyncing because the core writes files at shutdown that tell it where it last touched the wallet dat and other information and when the other core alters the wallet files and then the first one comes back, it will be pissed that it is not as it left it and probably want to resync.
Propably you would have to edit the code slightly and compile it yourself to get it running, so the problem you mentioned won´t appear
