When teaching recall to my two while out, I have a pot that rattles and in it there are fish4dog squares, cubes of cheese and a few fish star treats. I let them get so far ahead then rattle the pot, they come back (not always at once, but good enough for what I want - maybe a couple of rattles are needed) give command 'sit' and give them both a treat. I then send them on their way again and repeat it over the course of the walk. Sometimes putting the lead on, and taking off again - others not, or they think 'oops end of walk', every time I call them back. I also play a game of hiding behind bushes etc., and calling them to me.
It's not perfection, but works most times. It helps that neither of mine want to miss out on what the other is getting