hello nismo....
your car is designed to have the cells arranged in a row so each cell sits in one of the slots on the chassis, for security and also when developing these car`s the cell`s positions are fixed to regulate the centre of gravity for handling and driveability. When purchasing these cells from a shop, spend the extra £4-£5 and have the shop assemble the cells to your configuration, normally saddle pack, two lots of three cells joined by a heavy guage wire.when assembling the cells into a pack, the cells are actually bonded togethor(using cyano) while sitting in a jig (to keep them all straight and true) . this keeps the cells togethor, and allows the cells to sit in teh slots and hence keep the centre of gravity low.
most on road ( and off road ) 1/10 scale racing chassis are designed to use this set up.
i dont think there`s a stick pack mod available but i`m sure some re-useable cable ties could be introduced to help if you require.
Adz..