IMO the "no free lunch" thing applies here.
If you start to cut into the impeller, you will get more turbulence, but less flow, and most likely you will throw it out of balance which might cause a noisy, vibrating pump and over time mess up the impeller.
What do you want to accomplish? This pump is already pretty good in smashing up bubbles, and if you add the sponge on the outlet, most of them are being dissolved almost immediately. Have you tried simply turning up your CO2?
If the levels in the tank are too low for you, consider adding a manifold and add a second needle valve and Mini Elite.