We have a combination shower/tub enclosure in our bathroom here in Norway. The floor drain in our bathroom was placed in a very unfortunate location, such that the water draining from the tub/shower must travel nearly horizontally about 1 meter before it gets to the drain. This incline is too shallow for proper drainage to occur. Due to tight spacing, moving the shower enclosure is not an option. Moving the floor drain would involve a tremendous expense and hassle (breaking up the floor, redoing the entire electric tile heating system etc). What I'm hoping to find is some kind of pump I can place inbetween the shower drain and the floor drain in the space underneath the tub. This pump would sense when water came in and turn on automatically to assist the drainage, then turn off when it had pulled all or most of the water through. Does such a thing exist?
I have never seen it done in your application, but I bet this would work. Maybe a marine masserator (sp?) pump installed in line with your floor drain would work. These are relatively small units, run on 12VDC, and can pump solids and liquids several feet. They normally are not self actuated unless attached to a holding tank with a sensor, but you could install a switch to run the pump while shower is in use. This may not be the best idea, but I don't know of any units specifically designed to do what you are asking, without a holding tank.
This almost sounds like a common problem with draining RV holding tanks.
You should try to support the drain hose from the tub so you have a gradual slope reaching from the tub/shower drain to the floor.
I have a contraption called a "Slunky" which basically allows my RV holding tank drain hose to be very gradually sloped all along its run to a septic or sewer cleanout.