I don't know if this has been suggested before but how about having traps available to place along the path? It could be a gnome shop item.
I thought about it when someone here mentioned kamikaze sheep in another thread, well why not? Go to the shop, choose the kamikaze sheep from the list of traps and place a few on the path?
There could be a variety of traps, they don't all have to cause damage like a traditional spike trap, it could be a pitfall that drops an enemy or two (or more) further up the path, so basically the opposite of the god kings quicksand power or a man/woman with a free hugs sign that hugs (or pets) an enemy for a few seconds (soooo a non violent barracks/reinforcements)
There could be traps like the meteor power that annhialates the enemy (I was thinking a trip wire that once tripped sends a giant boulder rolling down or opens up a dam and wash them down the path) or damage over time traps like a small acid lake (like the necromancers special ability).
More than anything though i'd like to see crazy and silly traps like the kamikaze sheep and free hugs person mentioned earlier.
Any thoughts on this?