Thanks for posting! As daunting as the amount of work I'm going to have to do to achieve this is, sometimes the most difficult thing is making sure I believe it's actually within my grasp. To that end it's really nice to hear from someone who succeeded in a similar situation.
Regarding your advice: I had hoped to avoid paying for classes until I was actually in a degree program (supporting myself and a full time student means money is tight), but if that's what I need to do then so be it. At any rate, I'm open to any other suggestions you might have - I feel like I should be doing anything that might help my resume at all.
I have a couple of other questions for anyone who might know the answers or have suggestions. First, if I'm to enroll in courses, what are the most important ones in the eyes of an admissions committee? Also more specifically, while I know that doing well in a graduate level class looks infinitely better than undergrad level, I've noticed during my math subject GRE studying that I have no background in abstract/modern algebra. Would taking an undergrad level course in that be beneficial or should I stick with grad level courses?
And finally, is there any specific etiquette involved when contacting members of admissions committees at schools to which I might be interested in applying (or should I avoid it altogether)? I feel like they would know better than anyone how I could help myself, but I wouldn't want to hurt my chances at getting into their program farther down the line.