The matchplay can be used in conjuction with a bet from $5 to $50. So, to guarantee a win:
1. Bet $75 on the Pass Line.
2. At the same time (come-out roll), bet $50 with the matchplay coupon.
3. Bet $3 on Twelve.
If the shooter makes a pass (win), then you will get a $22 profit. If the shooter doesn't make a pass (loss), you will still realize the same $22 profit. Exception: if the shooter rolls a Twelve on the comeout, you will make a $15 profit, and your Don't Pass bet and the coupon will stay intact, so you can replace your Pass Line bet (a comeout Twelve would actually be the best outcome for you).
I've done this by myself dozens of times in various casinos, and only once was I ever told that I couldn't bet both the Pass and Don't Pass at the same time. I asked, "Why on earth not?" and the nimrod numbnuts pit creature in an ill-fitting suit couldn't say ("You just can't."). So fine, I handed the Pass Line chips to my friend and told him to bet them for me. I was waiting for Pitter Critter to tell me that you couldn't bet the Don't Pass if your friend was betting the Pass Line. Or your spouse. Or your child. Or your dog. (This was at the old Sahara, before it died a well-deserved and timely death.)
You of course would realize a slightly better EV (+$24, approximately) just betting $50 with the coupon and let the chips fall where they may, but I have this psychological aversion to losing in the process of taking advantage of a promotion (I lose, and then say "I never would have bet that $%#%@ $50 without the ^&*%$ coupon.").