Well... I'll give it a try. I have a feeling we'll be facing a similar situation come NYE.
Absolutely, have a convo with the groom to get all the poop on Dad that the groom feels is relevant. Ask when he'd like the dedication done, how long it should be etc. And run your final draft by him, just so he knows what's going on.
It's never easy to stand before an audience and honor a loved one who is no longer with us. But it can be done with tact and reverence.
Just some thoughts... you may wish to let the preceding song end and pause for a few seconds of dead air before continuing. This will get the attention of the audience.
You could begin with something like this: "My friends, (groom's or B&G's names) wish to take a moment to pay tribute to (Dad's name) whom as we know is with us in spirit tonight."
(If details are desired, insert here.)
Close with "This song is played in honor of (Dad's name). We love you and miss you, Dad."
Try to avoid negative words like don't, isn't, wasn't etc. Speak of the man in the present tense as it is his memory that is being honored.
Thoughts?