Suggested interface: each ghost follows a circuit, which resets to that ghost's default circuit at the start of each level. Change these circuits by choosing a ghost then mousing (or equivalent) a legal path from somewhere on its current circuit to somewhere else on that circuit, or to somewhere on the new path. The ghost continues on the old path until it reaches the point where the new path diverges, then follows the new path. Thus one can either substitute a segment in the ghost's current circuit, or ask it to follow a route to another part of the maze then begin a new circuit there.

The above semantics would prevent the creation of circuits that crossed or touched themselves, but that might be the kind of arbitrary restriction of which interesting gameplay is made…