How about flavoured bottled water - some is syned so check before hand. Does he drink tea or coffee, he can use the milk from allowance or syn it. Bovril is not tooo bad taste wise. Options or highlights again its syned but not bad.
Sauces, if you want a tomato sauce, make it yourself for free. Use canned tomatoes or passata or both, add onions mushrooms etc anything you want, and serve over pasta. It only takes mins to make so is just as convenient as a jar.
Creamy sauces, add 0% Greek yogurts to the final dish or creme fraiche (sorry can never spell it)
curry sauces, use spices to marinate meat/fish in, add water when cooking and thicken with some yogurt or cornflour and syn it.
Hope these give you some ideas.