Does the Sprint accept S X S packs?
They are much better in the long run.
If you can't find any you like, Trinity makes a shotgun pack kit that allows you to put 6 cells into shotgun configuration the easy way. Then again, you could just tin the end of 2 rows of 3 cells and put the iron in the middle, then pull it out really quick and slide the cells together, but the kit might be easier.
I use S X S packs, but there are some cars (Tamiya mainly) that I have that require shotgun packs. The vintage cars I have aren't really for racing, so I don't need huge GP matched packs for them, but in all my racing vehicle I have GP matched packs from Trinity.