Renaming for derivatives on export

[ashleykaryl]

Having read the DAM book my Raw files are named like this: Karyl_Raw_120415_V5F7835.dng. All I want to do is have Lightroom automatically insert Der in place of Raw in the file name when I export to a different format but none of the file renaming options seem to manage this. Does anybody know how this is done? At this stage I'm doing it afterwards using an app called Rename or I change the name manually when saving again from Photoshop but I can't help feeling they should already have the Der identifier when exported from Lightroom.

Thanks

Ashley

[ashleykaryl]

I forgot to add that I am using LR4 but I don't think it has changed since LR3.