I usually walk in the mornings and sometimes on an afternoon. On the days that I feel less than enthusiastic about it I tell my "Just 5 mins. Just get out there for 5 minutes and if you hate it, you can stop." So I put on my shoes and head out the door. I never want to stop after just 5 minutes though.
But presenting the idea to myself that I
could stop
if I wanted to is enough.
I take the appointment idea a little further by setting up an actual appointment with a trainer. I figure the workout programme has been written and the time set , so I will go. If personal training isn't an option you could try finding someone who will workout with you. I've found that I'm less likely to cancel if someone is waiting on me.
And after a while, if you're consistent, you may find that you don't need the extra push. You will want to exercise because it feels odd not to exercise.
Best of luck on your journey