So, not really. Honestly most animals are very androgynous prior to puberty - even humans. As adults rabbits have some sexual dimorphism in head shape, body shape, dewlaps, but until they grow into that you just gotta have a look see.
Instead of looking for another way to sex them, consider another way to CATCH them. How are you feeding them? I feed into bowls 1-2xs a day. Because of this I get hands-on interactions with each rabbit daily (albeit mine are in cages not roaming).
If you feed once a day, you can easily get every rabbit in the pen into the same spot every day. You can even still give hay free choice all day anywhere in the pen, just give pellets and veggies once a day.
From there it's much easier to, say, have them all eat in an area that's easy to partition off like a dog playpen and when they all run in to eat you just close a door behind them. Suddenly it's much easier to grab them than if they're running loose.
You could also consider some sort of fine net on a pole, or herding them into chutes.