....I'm looking to sell the car so that's why I was looking into borrowing or renting someone's grid charger. I wasn't sure how complicated the wiring was for this. I'd need to buy a harness and install it.
Seems like you should be able to get the car to charge it and not worry - earlier you said you disconnected the battery (I assume 12V cable) and the IMA light went away. So is it still gone or what? Basically, try resetting and letting the car charge the pack on its own (i.e. reset by pulling underdash 18 fuse, start car, rev to 3000 RPM and hold there). If it takes a while to reach Insight-full (i.e. 75%, 81%, 19 bars) then consider it fixed and sell the car... If not, then try grid charge...
Personally, if it were my car/situation and I didn't want to spend cash, I'd probably try discharging the pack with a light bulb (free setup) and then try charging with car, and if that didn't work I'd then try grid charging. Maybe some time in not-too-distant future I'd repeat the deep discharge and grid charge...
Also, I'd probably just buy the right-powered LED driver for the charger - like a Mean Well LPC-100-350 or LPC-100-500 (I prefer the latter) - like $30-40 total (try Jameco or Powergate), and I would charge on the big leads on top of pack with key on - i.e. attach some alligator clips to the DC output leads on the power supply and clip them to the big pack leads on top of pack, turn big circuit breaker back on, turn key on, put 12V charger on 12V battery, plug in power supply/'grid' charger (you'd also have to have put an AC plug on the power supply input leads)... This all seems easier and cheaper than fussing with a 'harness', a piggy-back spade connector and reaching down between DC-DC and pack to attach, and spending $300+...