You should still go with iControl... If you lose connectivity to the BigIP, what you may lose is some data granularity for the time period in question. You can still calculate rates for the time when you lose connectivity.
I suggest that you download the Perl iControl package, and do some testing. I think you will be surprised. (There is a very good collection of iControl info on this site to get you started).
Cheers,
Brian
P.S. - Running home grown apps on the BigIP invalidates your support and purchase contract. (Personally I'd rather have the peace of mind knowing that I am running a supported configuration).
Nimbostratus