Obviously two options – don’t report it, or report it.
Worse case scenario is that if you neglect to report it, the IRS may send you an amended return indicating that you missed that item. That’s actually happened to me about a decade ago. I think I ended up writing a check for a couple of hundred dollars. But that was for a VP win at a Strip casino.
If you report it without a w2 form, then it may create more questions from the IRS side. You’ll have a line item of “$5,000” in Other Income – it just feels a bit too pat. But that’s just me….