Given delegates with a certain type of amnesia (i.e. they should not remember to have voted on an issue before, although they might have to remember some binding agreements (I am not sure about that)), we could replace a plurality vote with an elimination runoff, where at each step of elimination delegates think that this is the only vote on that issue (which is thought to be affected by randomization) and they are not allowed to introduce new options.

Well, this system might have its own disadvantages, possibly similar to these (however, at each step negotiations are allowed), although delegates wouldn't know how to actually game it.