[McStinky]

How about viewing this as an algebra problem. Let x be the % of time you have trips or a boat in this spot, and let y be the % of time you fire a second bullet as a bluff on the river.

If he decides to call you down all the way, his EV is:
x(-550) + y(675) + (1-x-y)(275)

If he decides to call on the turn and fold to a bet on the river, his EV is:
(x+y)(-150) + (1-x-y)(275)

You need to find an x and y such that both of these come out negative. I whipped those formulas up really quickly and the details may be off, but you get the idea.

I guess you have to account for the possibility of him using a mixed strategy too, but this is too much math for me right now.