DJM900NXS2 mic or send return as 5. channel??

Hello,

I buy a djm900nxs2 this week. I really love the sound and the effects but is there any way to use the mic or send return for a 5. line channel? I will use it for Ableton but without using one of the 4 main channels because I need them for Traktor decks 1-4. 

Switching between the sound cards is no way for me. It disappoints me a lot that the dim mixers only have 4 usable channels! 

I hope there is a way!

Thx