Yes, that's the basic idea. By making high variance bets to begin with, you either lose or bust quickly, reducing average wagering. If average wagering is cut in half, then EV loss over the wagering requirement is also cut in half.

Consider a $100 100% Clearplay with 30xB wagering. For conceptual purposes, consider what would happen, if you bet all of your bankroll on a particular roulette number prior to starting wagering (I strongly recommendnotdoing this, this is only a conceptual example), then complete wagering on Loaded. You win 1/37 times and lose 36/37 times. The expected loss during remaining wagering is slightly over 100% of bonus, when wagering is done on Loaded. I'll assume 100% for easy math. This makes the EV of this strategy (1/37)*35*200 - (36/37)*100 ~= $92. Note that this is also equals bonus - average wagering * HE = 100 - 200*0.027 - (1/37)*100*~30*~0.035 ~= $92. Now instead of betting on roulette, think about what happens if you made high variance bets on slots.

Note that you can continue making high variance bets throughout the wagering if you want, but the bets towards the start of the wagering are the ones that have the greatest effect on EV since they lead to the greatest decrease in average wagering. High variance slots tend to be the 5-reel ones with high paying bonus rounds. Low variance slots tend to be the 3-reel ones without high jackpots.