That's adorable - -but I personally can't stand e-cards, they just lack the personal touch, and it give the appearance of no thought being put into the act.. like it was last minute (I know it's not the case, it's just the perception)
why not sneak a card or two into places that you know he will find them... His briefcase, the pocket of his coat, put one on the front seat of the car or on the dashboard... Be creative. Be sneaky.
