Yeah I did too, I have old Honda Dream perches on a 3-speed handlebar and it's tight. I cut down the throttle tube and made grips out of old couch lather wrapped around the bar ends. I had some old bar weights from a street bike that I put on the end to get some more length out of the bar.
For this new bike I am building, I have a set of old Raleigh motorbike levers and one has a thumb lever that will be my throttle and I can use a set of real vintage bicycle grips I have.