Virtual Hosting With Proftpd And MySQL (and shared key authentication?)

[wanabewired]

Hi,

I'm currently running an etch box with a proftpd setup as shown in "Virtual Hosting With Proftpd And MySQL incl quota" but was wondering if there was any way of including shared key authentication through ssl for virtual users? I need some way of controlling where an account can be logged on from and as my clients IP is not static, the only other way I can think of acomplishing this is through shared keys.

Does anyone have any thoughts or suggestions? Any help would be much appreciated.

Thanks
wired.