Can you put check valve in fuel line. My 2000 Wrangler starts hard because pump loses pressure after sitting a while?

You shouldn't be losing pressure, if you are there is something not working correctly.

Check your fuel pressure regulator, that is one place where excess pressure is routed back to the fuel tank, and where a malfunction could make you lose pressure while the vehicle sits.

Another option would be to let the fuel pump run a few seconds before starting the vehicle.

The regulator, check valve, and pump are part of the same module in the tank. Either replace the fuel pump module or cycle the key before starting ot prime the system.