Hi Tourist,
I'm sorry that no one has provided any information, but I'll offer this:
You can ask the known providers such as Asian Mystique or other providers if they will offer this service. Other independent providers may offer this service if you ask for it. I can't imagine that they would say no, but I fully expect that you would pay the same full rate despite only wanting the 'date' option without the private time at the end.
All that said, I can count on one hand how many times this question has come up. One independent provider that has since retired used to provider a 'social' option at roughly 10,000 yen/hour, but she was the only one that opening advertised that option.
Your best bet is to contact the agencies or independent providers to see if they will do this for you. I wish I could offer you more concrete advice on someone specific, but I can't at this time.
Last but not least, you could also try some places like Metropolis classifieds if you just want to find someone to go on a dinner date. Your results will greatly vary of course...