How do I get stirrup leathers onto an English saddle?

I'm cleaning this really old English saddle for a friend, so I took the stirrup leathers off of it. Now I can't get them back on. The stirrup bar is really old and probably hasn't been moved in a while, so I can't flip it down. I tried prying the leathers on with a hoof pick, but that only scuffed up the tips of the leathers. Help?