"Portfolio" forex charting + OANDA

I want to be able to chart, not a single pair, but a combination of pairs. For instance:
GBP/US-EUR/USD+USD/CHF-2*USD/CAD

I would also like to see it in real time if possible. Offline will also be useful.

Is it doable on OANDA or anywhere else?

 

I don't think Oanda offers this, but I would be interested in something like this as well.

 

Good to know. I thought I was alone in my charting needs!

Forex brokers: reply quick to this question. It would help your business to just reply.

 

Easily accomplished with E-Signal's GTIS feed and their "spread quote" which allows arithmetical operators.

 

You could write it as an indicator in MT4.

 

I just want to say many thanks for every body who answered. Very useful information. I am positive that those of you who answered may have a good idea of why I want to chart the portfolio, but if you are curious I will be happy to share with you (just PM me). I would also like to thank all those who will provide new tools to do the same (particularly free tools). Best wishes.