Ben,
This is how you do it.
When you get to the track you will wanna discharge at 20-30 amps like you stated.Being the pack will only be 10-25% charged it wont take that long and wont have as much heat as a fully charged pack.
If you race on Saturday I suggest doing this on the night before so you dont have to wait 2 hours before charging each pack.
If you race on Saturday simply get your batteries out while watching T.V. or whatever your doing and start discharging them down to 5.4 per pack.
When you get to the track on Saturday simply take the packs out and place them on the discharge tray.I even take one to two packs with me in the front seat and have them on the tray before I get to the track.That way they have a lil time to cool off from whatever heat the tray may have caused(Slim to none).Charge the pack,run it and then if it's only going to be one weekend before you race again and IF YOU have a spare charger not charging throw 200-300 seconds in it.If your not going to race for 2 weekends then throw 500-700 seconds back into it.
With the HIGH voltage and LOW resistance these packs have they discharge themselves faster than anything.
Some guys will race,discharge their packs down to 5.4,then tray and then put seconds back into them.
I dont think this has any more benefit than just leaving whats in them and adding to it being the packs will be sitting for a week or so.
I hope this helps.
Les