Be creative!  I just ran a P-40 yesterday on a stand and just used a garden hose fitting on a large piece of heater hose shoved into the outlet side of the water system in front of the prop.  Not correct but it worked for what I needed.  Might be able to make something to cover the portion of the lower unit where the pickup is possibly?  Forget as I only just bought my first PO a week ago and haven’t tinkered with it yet.  
Keep us posted if you come up with something.