GS functional group header - Gentran

[vzxkq7]

I'm using Gentran 4.0 and creating 820's for a specific partner. Within the 820's, there is a batch number. Currently, when I create my outbound EDI document, it has all the 820's within 1 GS/GE functional group. What I need is to split the 820's into batch numbers and create a GS/GE for each batch number. I have been playing around with the standard rule --> update --> current partner, but no luck. Does anyone know how I can use the batch number as the key to group up the 820's instead of just the partner.
thanks