LDO ground with Diode for temperature Drfit compensation
If you add a single resistor to drive a few mA through the 6-1 diode then you'll be a lot closer. 

The problem is that the voltage across the diode will be much less at 25~100uA than at 5mA. At various temperatures, it looks like the typical difference will be in the 100-150mV range (Fig. 1). As well, I'm not 100% confident that those numbers are not a bit optimistic. You might want to grab the SPICE model and do some simulations, but of course that will only tell you the typical behavior not worst-case.  

The MCU current drain is likely also highly variable. 

There are probably better ways of doing what you have in mind, but if your application will tolerate a few hundred mV difference maybe this is a usable solution.