I made 5 gallon batches with a 5.5 gallon pot using BIAB and sparging. There is hope for you yet!
My process looked like this:
Mash in my 5.5 gallon pot.
Pull the bag out and let it drip for a minute or so.
When the stream of wort slowed to a drip, I would slide a bottling bucket under the bag and lower the bag down in.
Dump in my 170-175 degree sparge water (serves to mash out)
Mix the grains and sparge water and let sit while I start to bring the wort in my pot up to a boil.
When the wort in the pot starts to boil, drain off the (batch) sparge via the spigot on the bottling bucket and add to the pot.
While doing this, I would live dangerously and boil 4.75-5 gallons of wort. Very little room for error or I would have a boil over, but this would allow for a near full boil. As some of the wort would evaporate off during the boil, I would just keep adding my runnings from the bucket.
In this thread
several people have mentioned their method, just try to find what works for you.