Is this the version with the venturi the size of a toilet bowl? If so just get a pressure fitting and drill and tap the backplate to match the fitting. Make sure that the fitting is flush on the crank case side, to prevent the connecting rod from hitting it. Also seal the pressure fitting threads.

The other alternative to using a pressure fitting is to use a Pen bladder for pressure.

If it is the one with the small venturi, it won't work well on high pressure.