Do you think he would wear a dog tag style piece? You can get handprint, footprint or even fingerprint stamped jewellery items. They send you the kit to get the prints (DH did one for me with Moo's handprints on a pendant) and they size it down to fit on the piece you have chosen. I know they do cuff links and stuff like that for men, but maybe a dog tag is more up his ally?

Or how about a digital photobook? You could do a year per double page spread if you have access to his childhood pics. You could add in little funny stories etc. I did one for DH for Fathers Day once and he loved it, though it was more about him as a Dad.

Will keep thinking!