We had the same dilema. And the solution was rather simple:
MLM= 64999 Kg --- and Caa was informed and aproved this.
Also we were asked to use flaps 40 in order to keep Vref below 141 Kt when flaps 30 would require a Vref above 141 Kt.
Given all this consideration we operated 737-800 for cat C.
Hope it helps...