hey matt,
on the flop i like to bet it super-tiny. its obviously still effectively giving a free card, and building the pot a bit, but if he has flopped a flush and is really quite bad i think he will give it away physically a large proportion of the time - i know that you have a very good read on the game so would feel confident on picking up on super-strength.
then, assuming he has just called the flop (i would pass to a raise) on a non-diamond turn i would bet 3/4 pot. this way the pot he will fold a diamond (unless he has

or similar), plus the pot is not too large so if he has you beat you can still get away fairly cheaply.
on a diamond turn i would check-pass against this player who we are confident we can beat in later pots
on this river it feels like you must be beat, and i would be amazed if he does not have a diamond (QQ or similar - surely he would raise the flop, even if he had limped pre), but it is a possibility. however, you say you feel he is weak (i.e maybe has the

or

). Many players would just call off with these hands if you bet 50-75k on this river. Against a better player i would bet the pot, but against this villain i would give up (as you can be fairly confident you will out-manouver him in later pots)