I vote for asking your DD for the future in-law's phone number, and calling the hostess. Tell her you're unable to be there, wish you could, and wonder if perhaps you could show your goodwill by sending flowers along...

Or, write a note to your daughter (or to the entire company), and send it to them, asking them to read it aloud on your behalf, in order to convey your good wishes to all there. (flummox them all by adding a nice sentence of praise for your DD's mother)

Or, if you've been invited and declined already, just use the address from the invite to send flowers to the future in-laws as a goodwill gesture.

You might also, if distance permits, simply invite the groom's family over for dinner, so you can meet them. Normally, etiquette says that the groom's family is to extend the social invitation first, but folks don't usually know this. And anyone who has a social impulse should follow it.

In fact, I think this is such a good idea, if I were you, I would do it even if I were attending. If I were the hosts, I would be very impressed and grateful. I'm going to remember this.