Awh, I'll be in that situation next year, and i'm not looking forward to it. I know how you feel, my husband has yet to be with my for my birthday and we've been together 4 years!!
Maybe take a pic of you and the kids today, on father's day, going to the park or having dinner and write something like wish you could've joined us! and mail it to him as soon as you get his address? And maybe send him something that's in the picture, or related to the picture..just an idea!