XV Lens Adapter screw in filter

[grotte]

Looking inside and taking some measurements it appears to me that the XCD side of the adapter has some tread in it and may accept a 55mm filter. One option I see is to drop in the filter from the wider end and attempt to screw it in, but this may be tough as the inside edge is conical and the filter tread may not reach the adapter's groves. Another option is to attach the filter at the camera's end. But then it will stick out 3-4mm into the camera. That's probably not ideal either. Has anyone tried this? Thanks!