the reflection map just follows your UV mapping. If you don't have a texture mapped in SU, then you won't have control over how vray determines your mapping. You'd need to add a dummy diffuse layer to control mapping. In your case - I'd put the reflection map in your SU texture, then in vray material editor do the following:
add a second diffuse layer under your first material
add transparency to your first diffuse layer by specifying a "TexAlpha" material set to white.
This will allow vray to apply the UV mapping you've set in SU, while ignoring the pattern in the render. There's more information about this on the ChaosGroup forum if you need:
http://forums.chaosgroup.com/showthread.php?62274-Texture-placement-workaround-for-SketchUp
