I don't know if it is or isn't possible, but from your report here I guess it isn't. The only possible solution that I can think of is this: try setting the plugins to use the embedded JPG (instead of the raw data) to create a thumbnail. See under Options | Digicam and Options | DCRAW in the main menu.
The DCRAW raw development code that both plugins are based on, is no longer being maintained. So, I don't see how ThumbsPlus will be able to decode new raw formats from new cameras unless Cerious switches to a different raw library.