YES, you can hook up the hose to the seadoo and have them run for up to 5 minutes. Connect the hose and start the seadoo. Turn on the water after it is started. Turn off the water, than shut down the seadoo. This way it won't allow water to back flow into the engine through the exhaust due to no back pressure from the engine not running. The bearings and seals on the impeller jet pump are cooled from being in the water. When it is on the trailer it doesn't have that cooling effect so they will get hot after about 5 minutes.I pre start my seadoo's too, dry before I leave for the launch too. Just for a second or 2 to be sure it will start at launch. Peace of mind is worth lot.
You could try to tip the doo up to get the water to the exhaust away from the engine. If you want you could join as a "premium member". As a premium member you can down load a authentic seadoo manual from the seadoo manual library. In the library is a variety of manuals for almost all years and models. You can view as many as you like on line as a PDF file, or download it and print it for your personal and privet use. There are operator manuals and repair manuals for you to do your own repairs on your seadoo. The repair manuals have everything from troubleshooting, repair procedures to winterizing. It contains wire diagrams torque specs and pictures for disassemble and assemble instructions. In the spec sheets it tells everything needed to maintain oil changes, spark plug gaps, carburetor rebuilds and impeller wear ring tolerances. Click on the "Seadoo Manuals" link at the top of the page for more details. If you need any help or get in a jam, we are always here to answer your questions too.
Karl