Best way to redeem CSR points at 1.5x before closing card?

My wife has had the CSR for a number of years, but after the fee hike we decided it makes sense to switch to an alternative, so she's planning to downgrade in a week or so (AF posted mid-Dec).

Despite trying to spend most of the accumulated UR points, she has ~30K that are still redeemable at the 1.5x rate for travel booked via the Chase portal. That's actually been the main way we've redeemed points previously; somehow partner transfers have rarely been attractive for our travel pattern.

I was wondering if there's a good way to "lock in" the 1.5x redemption multiplier on those points (i.e. extra ~$150) without booking specific travel? We thought about booking a refundable flight on an airline we fly often, and then canceling the flight for airline credit (or even cash)? Might work in theory…but maybe that doesn't because the cancellation would need to be processed through Chase Travel – rather than directly with the airline – and would always result in a points refund rather than $ credit?

Would welcome any advice. FWIW, plan is to CP to Freedom, keep the UR points around, then most likely sign up for CSP some time later for a potential SUB (and ability to do partner transfers again).