This may be too much of a hassle for you but what you could do would be to put in a divider acting as an overflow in your sump with a piece of plexi glass or glass. This would hold back enough water until it reached the overflow level and would ensure that your skimmer would always have sufficient water level. I have a wet dry that I am using as a sump and the way it was designed was such that the overflow box fills this compartment first and skims in here, overflows to the bioballs and then into the main sump. It works really well. HTH