Forcing a camera to ignore transparency?

I'm developing a racing game for mobile, and am implementing real-time reflections. The reflection camera uses the vertex-lit rendering path, but it still lags, and checking the profile and some tests revealed that removing all transparent objects from its view got rid of the lag. However, I still want the transparent objects to be visible in the reflections. Is there a way to force all transparent objects to render as opaque (and thus be part of the depth buffer) for one camera only?