Hi,
Cool that you have a JRT, I love them and have a housefull of them
There is one game that you can play that has multiple benefits which should help.
At meal time, take a kibble and roll it gently away from him, but only a few inches and say 'Get it'.
Roll the kibble one at a time and roll many of them. He should see start to chase them. As he understands the game, you can roll them a little bit further, but always remember to make sure he sees the kibble rolling away.
The other benefit is, when he turns back to you, say come/hear, which will re-enforce his recall.
You can also use any food that will roll, just not his kibble.
Once he is comfortable with it, you can also hold him back, roll the kibble/treat, then release him to a 'Get it!" etc.
You can also get a small plastic water bottle, poke a couple of holes in it, fill it with some very high valued goodes, i.e homebaked liver works great.
Open it and pour the treats into your palm slowly, letting him take them as they come out of the bottle.
Then put a light cord on the bottle, roll it away from you and tell him to 'Get it". The cord on the bottle will stop him from running away with it lol.
Nicely reel him in and reward from the bottle.
It shouldn't take long before he starts picking it up.
Hope that helps.