Nothing will be as cool as fellow fish or octopus following you around. If you fed them they will recognize you and may learn to follow you around... just hide the food (or perfume... tuna oil or like) on the belt, special neckless, the foot pockets... or something like that.
You could leave behind a cloud of this shiny stuff the girls use on makeup... a kind of magic trail.
And about to hide a tank under or over the sub, and while changing sides have a little discrete breathe... just to keep under more time than anyone could imagine (don't forget the computer).
Build thin gloves with membranes in between the fingers... good mobility and will look impressive if you stick a hand in front of the pretty girl.
Leave a present from the depth for the kids or again the pretty one!
Use a scooter that you will leave over the sub to get faster under and back to the surface. A sub have plenty of dead angles you can hide in, learn them.
You could use makeup on the face... better than a three days old beard!
If you dont find blue for the material... paint everything shiny silver and bleach your hair; he could look cool and modern... easier for the googles!
Have a good blast, and queep us inform