You might try making a little cover or something from a 6" to 4" duct adapter. That way you can just pull the thing off when you have to pull the hoses out. Just need that adapter and some tin sheers, and you could just cut it down tighter to make what you need and then flange it out, so you can duct tape it to the wall and run the hoses through it. Or you might try taking a 4" piece of flex duct and just make a cone out of a small piece of it. Try looking at Home Depot or Lowes in the HVAC ducting section, and I bet you can find something that you can jerry-rig.