First, I'm shaking my head that you're a moderator at a sports gambling forum and don't know the difference between a cash and a matchplay bonus.
If you want to maximize your return (and if you did want to you made the first right decision 50% matchplay versus 20% cash) first check with the book about how you can use it. Presuming you can use it any normal way...Bonus Bet as a stake...you get any winnings....
Bet it either....
1. on a long shot dog, scalping with another book or
2. on a parlay (if you are a football bettor I suggest a 3 teamer)
As for scalping, a polish scalp at high odds is all you need, not a real scalp. Lets say its a $50 matchplay and you bet it at +800. At another book you have -850 (again no scalp but watch)...there you lay 357 to win 42. Either you win $400 and lose $357 netting $43 or you just win the bet at the other book netting the $42. Either way you just turned a 50% matchplay bonus into a 42 or 43% cash bonus.
Betting a 3 team parlay in football if you are flipping coins, you will win 1 in 8 times....they'll pay 6-1...so your cash value of your matchplay is .75 on the dollar (in this case with a 50% matchplay, equivalent to a 37.5% cash bonus).
See its that easy, Free money!
Was a bonus whore born tonight?