CCACHE recommends these type of valve extenders with next-gen lightweight tubes such as Tubolito Tubo/S-Tubo and Schwalbe Aerothan. They don't require the inner core to removed.

Precision machined aircraft aluminum Presta Valve Extender with leak-free o-ring seal. For 60mm or less, deep section rims.  

Specifications
Ideal for use with Tubolito or Schwalbe Aerothan tubes
Machined aircraft aluminum alloy
Leak free o-ring Seal

Mfr Claimed Weight
3.4g (40mm)

Note: Sold as a single valve extender.