While you can technically get more than one card (one per visit), they will only give you one if they know you've been there/ or remember you, and although you can enter the code a second time on the same account, per the rep you'll get charged (so yeah, use a different account).
As far as prearranging with a driver to pick up at LGA doesn't seem possible AFAIK-tried this and you'll just get fed the first driver as there is a que at LGA and they won't let you bypass it, except by maybe one car. That being said the guy I got was happy to work with me luckily
Got a more than $220 ride in a nice lux SUV including two trips to LGA (one for another promo card
, JFK, and getting picked up elsewhere in NYC, all for free. Gotta love these promotions and Dan's thoughts on how to maximize