Solvent cleaning is the only way I know of.
Long ago, the BVM website "Tips and How To's" column addressed this problem. It was aimed at using the BVM JetCase for airline travel.

I have used BVM's advice, and will report that it works well.

Simply drain ALL of the fuel from the aircraft.
Flush the entire fuel system with PPG DX330 "Acryli-Clean" grease and wax remover.
Drain the DX-330 from the airplane, and allow it to dry completely. Compressed air is not recommended.
Repeat if necessary, using fresh DX-330.
The fuel system should be now free of any kero or Jet-A smell.
Wipe the outside of the Airframe with DX-330 as well, then apply a coat of wax.
When the airplane is refueled at your destination, be sure to follow these BVM UAT instructions for the first start. This is a very important step. http://www.bvmjets.com/Pages/fuel_3_02.htm
Also, with the engine at full power, raise the nose and shake the airplane in order to dislodge any air bubbles that might be in the UAT filter media. Shake the airplane until you are satisfied that the system is purged of any remaining bubbles.