plinths on my kitchen cabinets
Really confused about what you are trying to do here. Your definition of plinths and mine must be different, as I can't follow their relevance to the bottom of kitchen cabinets. A photo would get you a much better answer here.
Also can't figure your angle dilema, unless you have some really odd shaped cabinet combinations. The vast majority of the time you are only dealing with 90 degree corners, and occassionally 45 degree corners. I'm sure what you need is pretty simple, but I just can't visualize your situation.