I would practice just walking, halting, and backing him up past the float with the doors open. If he rushes forward stop him, wait until he calms down and move him back one step and vise versa. Then just keep working him near the float.
After a while you can just ask him to take one step towards the float and halt. Then one step closer, etc. Then ask him to bring one leg on and stop, back him off and then ask for one leg then the other and if it goes well, call it quits for the day.
Also, when walking him forward don't look at him. Lead him forward like you usually would. Good luck!
"You know, for as long as I can remember, I've had memories." ~Colin Mochrie