if you are using a three line set up i think you can do this. for the refueling line, make it long enough so that you can hold your plane vertical on its nose and hold the end of the line above the tank. where the fuel goes up to should be the level of the tank. of course there will be some capillary action but minimal. that should give you some level of fuel reading. this will work as long as the tank is not pressurized so for Y.S. engines, you need to release the pressure first.

so if you are using a two line setup maybe you can set up one tube for that specific purpose. however, it is important to note that you have to release the tank pressure as well as take out the fuel dimple for it to work.

while theoretically you can do this with the plane level as well and the refueling tube vertical, i think the reading will not be accurate.