[Egregore]

You can tell startup that you have some unfinished project at the old job and you want to finish it part time.

If startup fails - I'm sure the old firm will take you back and even with a rise, because you'll have more experience. (I know some cases when people left one firm and then came back with a rise).

[hackDaily]

Well, that's an interesting solution Egregore. I'll have to take that into consideration, thanks for the input.