The Hello Lights site said you really can't. Here is their answer to the question.
*** FAQ:
Q. Can I run T5 bulbs on the ARO Model 4LX ballast?
A. Simple answer: Yes, the ARO VHO ballast will "fire" T5 lamps. However, T5 lamps are high performance lamps and requires strict operating conditions for lamp performance and reliability.
Starting: Proper starting and operation is crucial for lamp life and performance. One important parameter is starting - the lamp is designed to be started using a program start - this is an accurate sophisticated controlled starting with proper filament heating with precise amount of time before ignition voltage is applied to the lamp.
Operating Current: Lamp operating current must also be controlled to tight specifications for performance and reliability.
We do not recommend the use of ARO VHO ballast to be used with the T5 lamps. Yes, it will fire the lamp as with many other ballasts but this does not mean that the lamps are operating to manufacturers specifications. Many ballast manufacturers claim that their ballast "works" with T5 when in fact a dedicated ballast specifically designed is a must, particularly for the T5 lamps!