I have just played around with it, and unfortunately I can't see a way. You can edit in contacts, Person1 and set message tone as None, so they can't be heard when they message, but will still come up in iMessage on Mac, but because its all in the iCloud, if you block them in one, you have them in the other.
I think the only way to do it, is to delete them as a contact, and next time they message you, don't accept them as iMessage on your iPhone, but DO in iMessage on your Mac. I haven't tried this personally, but I know when I reinstall my iPhone OS it asks me if I want to use all my emails, and phone number as iMessage on my iPhone, and when I got my iMac I had the same option when I set up iMessage on that.
Is all I can think of Joe . . .