What are the ways to achieve disco lights moving over the subject.... in post ?

If we have a motion video playing as the background with lasers and disco lights , I want spills of random lights on the subject sitting in front of that background or green screen ....in the post .....what are the possible solutions.If we don't think that the light in the background is the source of that spill , .....it can be a light out of frame somewhere at the top which is not seen ,.....so with that concept , there can be random rays .....can you suggest ways to do it .....?