Is there any way for me to advance rank in while waiting to go to basic?

Yes, there are many ways to make rank before even heading to basic. My husband went in as e3. By doing some 'recruiting' and getting others to say that you asked them to join (and they DO join while you are in DEP) you will make rank. Also, there are education benefits (college or technical school). You already know about jrotc. Also, while in boot camp (at least Navy) you can pick up a rank by being a squad leader. I can't seem to find the site, but there is information on about.military.com. Also, talk to your recruiter. They will know the in's and out's.