What is the best strategy to use you Free Play Money?

I used to have a system to play 4 2-team parlay.

 

Let say I have 1000 free-play $.  I will divide it by 4.  So is 250 each.  and I will pick 2 games (side or O/U is fine) with the half line (-4.5 or O/U 155.5, so that there has to be a winner).  and then I will place a bet on 250 on the 4 possible outcome.

 

-4.5 O 155.5

+4.5 O 155.5

-4.5 U 155.5

-4.5 U 155.5

 

So that I'm guaranteed 650 from the 1000 free play.  so that is 65% return. 

 

Yesterday I made a deposit into a sportsbook and looking to do this again, but they has blocked the parlay.  So right now I'm hanged with the straight bet.  which will only give me 45% return.  that's $200 on $1000. 

 

So if you have any other strategy that pays more than 45%, please pm me.  If it make sense, I will send you a free NFL/NBA system that I have.  Thanks.