Analytics

I don't think Analytics or even an iRule is going to help you here. However, if ID'ing the actual users isn't required I'd suggest finding a statistics for layer four sessions (rather than TCP connections); this should give you an accurate figure assuming you're not using WA or doing anything interesting to increase performance. I'll get back to you shortly after taking a look at my VE.

Update: OK, I've not got AVR provisioned so sticking to standard statistics your best bet appears to be: Statistics > Module Statistics > Local Traffic > Persistence Records. You should then be able to filter on a particular Pool Member as required. Obviously each record represents one user.

Further update: Remembered you're using Cookie Persistence so this probably is no good. Standby...