Here's my tips for getting from Resort to Resort by using the WDW transportation - not the quickest way around, but you won't get towed!
From WL to POR: If possible, try taking the boat to MK, then bus to POR and the reverse. It will probably be a quicker trip than using the Downtown Disney method the resort will suggest. But after MK hours, this will be the best option.
Off site to WL: they can park at MK lot and leave their car there - there should be a bus that goes to WL (but check!!!!!) or Monorail to MK then boat over.
Off site to POR or WL: park at Downtown Marketplace, can use buses after 9:30am.
Hope this helps open up some options!
-Kim