The simple thing to do would be to select: Image > Mode > 8-Bit while inside Photohop to convert from 16-bit to 8-bit and all your filters will be available again. If you find yourself doing this over and over then perhaps you should just change the way Lightroom hands off images to Photoshop. Go to Lightrooms Preferences and Select the External Editing tab. Here you can change the bit depth for all images that are passed off for editing to Photoshop.
Both Lightroom 2 and 3 will allow you to setup an alternate editing program and save any settings there as a preset. That preset could simply be the same parameters as the first with the exception of the bit depth, thus allowing a quick way of passing off a 16 bit image when you need it.