How can I force unity webplayer to reinitialize for changed build unity version?

Our team is trying to change the build that the unity webplayer is targetting at runtime (based on button interaction) from a unity 4.3 build to an older project built in 3.5. We've noticed that the build loads and behaves properly, all custom shaders are working fine but any unity default shaders (ie. diffuse) are failing, resulting in pink everything.

When loading the older build (3.5) as the first build everything works fine. This leads me to belive that the unity player, when first initialized, is selecting versions of shaders to use based on the first build that is passed to it. In our case I assume that it is selecting the 4.3 diffuse shader, and when we load the 3.5 build later on it doesn't have a useable version of the shader to work with.

My question is, how do we force the webplayer to reevaluate which shaders (and posentially other resources) to use based on the new build unity version?