What I would do in your shoes is to use the BoA like you want to use the Discover- run a lot through it, PIF. Put a latte or a candy bar on the Discover every week or so, PIF. Do this for about 3 months, so you're building a pattern of reliability.
Then call Discover and ask for a CLI, "because your limit is just too low to even buy gas with it and not wreck your credit score". They should see your usage on the BoA, and hopefully be motivated to compete for your business...
To drag out the gardening metaphor, consider this Discover card as a very tender little plant, way more fussy than the usual marigolds and tomato plants that you put out. You're going to have to give it a bit more attention and water and protection and plant food than you do to the others.
With time and a bit of luck, it might bloom for you.
To get back to the more boring version of things, Discover is a bit stingy with CLI's. I'd take the CSR at her/his word and hang on until the 6-month mark. Use and PIF, use and PIF, and shine up your reports in the meantime. Good luck!
BTW, are you getting one of the fun card designs? You can even have more than one, so you can use a different one each time you whip it out.