I use a mobility scooter and walk a border collie. I use an harness with a bungee jogging lead and waist belt. I fasten the waist belt around the captain seat positioned so the lead is to the left side then JJ can walk on the pavement to the left. The lead is then behind you and you an shorten it by wrapping it round the arm rest so the dog can not walk any further infront than your front wheel. Drive so your on the road right next to the kerb and the dog is on the pavement this way its harder for you to accidently run over his paws as you'd have to mount the kerb first. With the scooter taking the dogs weight you then just move forward when he pulls stop, when he stops and looks and you, try giving a treat and say 'walk' (not heel, its not safe to teach heel command for scooter as they'd have to be too close to the scooter) if tries to go straight off into a charge stop again, it will take a while to get down the road the first time!
Once he starts off and relaises he can't get ahead of the front of your scooter he should start walking properly at side of you. Then you can go a little faster if he wants to move a bit faster. I'd be careful with him being a pug and them being known to have breathing issues, to not stay at full speed for long (especially if its a bigger 8mph scooter you have).
Once he stops pulling so much you can give him a bit more freedom in some places where its safe for him to have a bit more lead (to reach a grass verge for a sniffabout) or switch to an extending lead on a grass area if you don't want to let him off completely, then when you come back to the road put him back on the shorter lead.
I usually have JJ to the left and slightly infront but he's a bigger dog and can keep up a brisker pace. It's more like cani cross or bikejoring when we do it ..lol! ..but he does know how to walk very slowly when he needs to.
The commands we use are
left, right, stop, steady, slow, pace, go, still, go wide, stay close
I've just relaised the lead shown in the video was his older one. I use the Trixie walking belt with the bungee lead and he has an harness on rather than clipping it to his collar.