B-schooler,
I'll echo Stacey's advice here. When it comes to a lack of quantitative experience, and the various ways to remedy it, there's a bit of a pecking order:
1) Ideally you've scored above the 80th percentile on the quantitative section of the GMAT exam. This is a very strong way to signal your abilities. A high GMAT result (in both math and verbal), coupled with solid marks in undergrad (even in the humanities) can go a long way towards suggesting that you will be a solid student, that you are naturally bright, etc.
2) Another great step to have taken is to build an alternative transcript by pursuing coursework in subjects like calculus, accounting, statistics or economics and earning As. Some candidates take online classes, like those offered at the UCLA Extension School or MBAmath.com too.
3) Finally, your recommenders should support you in this regard by highlighting your facility with numbers/quantitative approach at work, etc. Your job descriptions and essays may also hint at the fact that you frequently tackle quant. issues, etc.
Since it sounds like you can likely check items #1 and #3 off of the list, the real issue is how you tackle item #2. While in an ideal world, you should have already taken the quant. courses and be able to share grades with the adcom at an eventual admissions interview, there are some other options. For example, you could pre-enroll for some courses that start this fall, and indicate as such to the adcom at the time of the interview (you might even have a mid-term grade at that point - if the interview is in October/November). You could also take an online course that starts now - or sometime in the coming weeks, such that you'll have it on your record at the time of application (and may even have a grade). The final option is to simply state that you "intend to pursue courses if admitted" to business school. While this isn't ideal, it's cetainly better than saying that you plan to 'wing it' once you show up in b-school (or saying nothing). There are also some ways to make the claim more convincing. For example, you might name specific courses, start dates, schools that you are looking into.
"Although I've learned a lot on the job, I am aware that my formal quantitative education is somewhat limited. As such, I've looked into taking both statistics and calculus at NYU's School of Continuing Education. They meet once a week and the start date is January 15th, so I expect to have a busy winter!"
It sounds much more impressive to say something like that, than to simply make an ambiguous claim. In addition, to the extent that you can pre-enroll for any courses, I'd recommend it - so that you can really signal to the adcom that you are serious about doing this.
Clearly, there is no substitute for having already constructed an alternative transcript of quantitative courses - but if you haven't, you're still better off showing a genuine interest in that coursework than saying nothing at all.
Best of luck,
Graham
