Can I use individual wires from romex bundle?
Short answer: NO

You may be able to use individual wires taken from a non-metallic cable (Romex is a brand) within a fixture, but not between fixtures or switches.

NEC 300.3(B) requires that:


  All conductors of the same circuit ... shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord [with certain exceptions that do not apply here].


If you give us a diagram of your fixtures and switches, we may be able to suggest a solution.