Hi Ryan,
if the customer understand the risks there are no problems. I do not see as "under the table favor" as you describe it. Usually test roll is processed before the customer bring in the actual rolls. Hand crank never worked for me. In order to process the film evenly, you would have to hand crank evenly until the end of the film is out of the Developer. That is going to mess up the Bleach time. Except for the Developer you want to keep the rest normal.
The bigger picture is that the Pro labs tha uses a dip and dunk processor is getting hard to find. In San Diego CA six large pro labs closed during the past four years. Only one pro lab with c-41 dip and dunk processor is in operation.
Germar,
things got little complicated but if you are really interested I think the information is going to help you. Let me simplify a little.
color push processing:
My choice is Fuji 1600. You can try 800 speed.
Processing is best done by Dip and Dunk processor. D&D processor can adj. Dev. time easily.
Always process a test roll. Results will vary. Do not push process over 3 stops. Images will look flat if you pass certain point.
B&W push process:
All B&W film processor has a variable developing time adj.
Try hand processing as recommended by Rico and Ryan. It is really that easy.
Contrast will increase when you push process.
I like the T-max 3200. Tech Pan if you can find it. It is excellent. Recording film if you can find it (golf ball size grain).
For larger grains do not use T-max developer with T-max film.