I've been thinking about a "work around" and am wondering about "modifying that #5 bridge" just for that one cylinder.

I wonder if you could have the #5 bridge's top surface, machined down about .017"-.020" = this will give you your clearance, for the jake brake setting.

I've never done this, and would have to measure thickness of the bridge's top surface metal, before trying such an idea. (Is it thick enough to have that much material removed?) 

A shop, with a valve grinding machine, should be able to "surface" a bridge's top surface, although normally you only remove enough material to "square up and smooth" the top surface.

You would only be out the costs,  of one jake bridge, if some didn't machine correctly.

Next, I just thought of a different plan, what about machining off .020" for the jake brake's  #5 slave piston's two vertical legs = that would get you your clearance.

Neither, of these ideas, are "by the book", but might work for many miles.