Just curious as to why you are in a hurry to get them harvested.  Is it a double cropping issue, and do you think it will hurry them along?  Since the beans are already turning yellow, I would say they are at maturity and sucking up minimal moisture & nutients.  ....only need sun & wind to dry them down.  What do you plan to kill them with....2,4-D or something else?  ....and at what cost? 

I'm not picking apart your plan.....just want to know some of the reasons for your decision.