Im just wondering is there anyway of splitting a really really big stack up?like into smaller stacks

only by transfering them

Make some new 5-pop stacks to help with this
Also bear in mind any transfer fees, or loss of troop level (if you're transferring into lower stacks, like fresh 5-pops ) - and the 90% BP needed on BOTH stacks to effect any transfer. It's a little tricky, but a spot of planning will get you through