It is a dude... who doesn't field a position. Doesn't even step on the field and stand around.
He just hits every ninth time.
It is definitely in the same ballgame (so to speak) as the Disco-Night glowing-ball uniform-shorts stunty lameness as starting your season a week early, overseas, and on at the same time as Coast-to-Coast AM is talking to Professor Batshit Crazy about whether the aliens will start the Rapture in 2012 or if it might actually be reverse-vampires.
Dude just kinda... hangs out on the bench when everyone else has to play the other half of the game.
Pinch-hitting a midget to draw an automatic walk is truer to the spirit of the game than the designated hitter because at least the normal substitution rules apply and when you pull him for a pinch runner, the midget cannot be put back into the game.
The DH is a pinch-hitter who gets to be re-substituted in four or five times a game.
Why not a holographic "shadow-man" for slower running hitters?
Bionic "Go Go Gadget Arms" for the centerfielder but he can only use them four times a game and if he uses them a fifth time, even on accident, it activates The Multi-Ball?
These are both things roughly equivalent to the bullshit nature of the DH.
It is still not quite as crazy as having major league teams in Florida cities that clearly don't want them, just to dilute the pitching talent pools and give the FSN channels in Miami and Tampa more programming but... it is reasonably close.