You want the "to Win" amount on the ML to equal the risk amount of the PL, so if they win by exactly one goal, you push.
An easy way to figure it out -1's is to use a parlay calculator. Google that.
Type the ML into the calculator, and then adjust the bet amount until the bet amount and payout add up to your unit amount. The payout amount on the ML will be the risk amount of the PL.
Most -1's will be plus value, but for the ones that end up minus odds, just adjust the bet amounts accordingly to the odds. For example, if your unit amount was $100 and you came up with $70/$30 ML/PL distribution and the odds came out to -122, just times the $70 and $30 amounts by 1.22 to get it to a "to win" 1 unit scenario, rather than a "risk" 1 unit scenario.
Does that all make sense?