I'm not sure if that's good advise in this case. The case where you don't get forgiveness in this case might mean that you put a ton of work into something and now much of it is owned by someone else.
This is one of those times that this adage applies. In the worst case, "begging for forgiveness" does not mean asking your manager for an exception. It means losing an expensive court case with your former employer about who owns your IP.
