got anouther idea for you, one I use all the time. Assign a new lambert to you your model, then create a locator. Make an attribute on the locator called x-ray or something like that. Parent this locator to your perspective camera, then use a set driven key which drives the transparency of your new lambert off of the locators x-ray attribute (which you created). Since you parented the locator to your camera, it will allways be there for easy access. You can drive tons of other attributes off of this thing too.