I’m leaving the ending alone; to me it would be a mistake to remove it in a fan edit. But it’s just MHO.
Here are two clips required in order to remove BB8 with the [Rich Evans] AT-ST [/Rich Evans]. The only problem, apart from potential less-than-perfect editing, is that we do not see BB8 explicitly rejoin our heroes until Poe cuddles him on Crait. Might be okay, though. I took a lead from Buzzclub (the German TLJ edit thread guy).
https://vimeo.com/263272913
and https://vimeo.com/263273045
passwords: fanedit
Those are pretty good there Hal. If there is someone who can do some good CGI work, it is possible (but difficult) to have BB-8 come out from off the camera while Rose and Finn run to the shuttle to catch up to them. The advantage of the possibility is it is not a close up scene, it’s from a distance. So a skilled CGI artist POSSIBLY could make something like that.