US Tourist Visa refusal under 214

So my boyfriend was refused his tourist visa to the US today as he allegedly doesn't have strong enough ties. They asked him if he had kids (no, he's only 26 afterall), where he lives and read his letter of employment. That's pretty much it. The lady said he would only get a visa if his situation changes considerably.

So he's obviously going to reapply with more documents. Here's the thing: he does not own or rent property (stays with his dad and grandparents), doesn't have a spouse or kids (again, he's 26 I don't know how they can expect that really).

So what else can he use to demonstrate strong ties? We were thinking cell phone contract, obviously the employment stuff that was presented, possibly taking out an investment? His car is in his name but is paid off. We were thinking maybe if he enrolls in a course next year that should prove that he needs to come back.

He also helps look after his wheelchair bound grandmother and contributes financially to the household. He has two dogs that are basically his kids whom he is solely responsible for.

I suppose the only considerable change would be one of property and/or marriage. We are in a long term relationship so I suppose its not totally out of the question. Seeing as I don't want to get married at all I would really not like to just for a holiday haha

Any ideas would be greatly appreciated!

Update: after the initial visa refusal he went to see a visa specialist and reapplied. He just took a lot more documentation with him than the first one, no other changes and he was given his visa :)