There are several cards that use a single controller, one that comes to mind is the HD7970. It uses the CHL8228 which does indeed have two independent controllers built into one IC. You can see in the datasheet HERE
that pin 6 is VSEN for core and pin 38 VSEN_L2 for MEM/PLL. Those are each independently controllable feedback resistances for increasing or decreasing the different voltage levels.
As for finding the feedback or sense lines without a datasheet that can be tricky. I have done is many times now but it takes diligence and some reverse engineering. I look at several datasheets by the company which are available and look for patterns in the layout. Then I make some educated guesses based on my findings and so far I have not killed anything. For beginners, if you cannot find the datasheet, or you cannot find/dont want to use internet mods...then its best to just not even go there.