Personal Experience:  I was trying to get a very generous severance package from a large telecom in the US that was being offered to those who were to be laid off, as I already had another job lined up.

I tried the routine you suggest:  I was insubordinate, condescending, arrogant, the whole bit.  I was *SURE* I was going to be the one laid off.

They **PROMOTED** me!  (I took the other job, anyway.)

Your actions are not always interpreted how you wish them to be.

Get your prospective employer to give you the 4 weeks.  If they're serious, they'll make it happen.  Put in your 4 weeks.  Tell your boss you'd like an early out if possible.  Hope for the best.