There's ram air (pressurized air) used to cool parts of the engine. If this air is vented through the rear of the engine, then some small amount of thrust can be obtained ("recovered") probably at some temp expense. This is similar to cabin pressure outflow recovery.
I believe on the IAE V2500 there's a thrust recovery outlet that's normally closed behind an access panel door on the left side of the engine. IAE = 49.5% PW
