SSL Offloading

I've started performing ssl offloading for our most of our applications, but have hit a snag, not with the offload process but with our application, that I can't seem to figure out. Our domain uses a CDN network to serve all images. This CDN requires us to use different url's for depending on http or https. Before the ssl offloading, the code was checking https in the ServerVariables. This is not going to work if the F5 is performing the offloading as this will always be set to false. I was thinking of creating a header variable and setting it to false under the http virtual server and setting it to true under the https virtual server. My dev team can then determine if ssl is used based on this variable. Does anybody think there is a better way?