Its not like its anymore difficult to solo this. As long as you go no further than the rocks directly next to the bridge where the hobgoblins spawn, you'll be golden. Deploy Dinklebot. Run to the topmost ridge to snipe. When enemies are down to the last few kills, jump down to the rocks just before the bridge and snipe from there. New waves spawn. Rinse and repeat. Easy, it just takes a little more time is all.