I am assuming that your SMI system does not have the "latched or real time" switch that is available on my SMI Silent Partner system. Real time mode would solve your problem as it releases the toad brakes when deceleration ceases.
A call to the Freightliner Help Desk might be helpful. You could ask them how to disable the brake light activation from the exhaust brake. 1 800 FTL-HELP. Have your vin number handy. With your vin number, they can look up your chassis wiring diagram and possibly determine how to disable exhaust brake light activation. They have always been very helpful for me, and it's a free service.
Fred