I have placed a filter holder ring object up on Thingiverse for those of you with these filters and a 3D printer.
Filter Ring for DJI Phantom 3 and CollegeGeezer's Die Cut ND Filters by Wolfie
It is designed to fit over the stock DJI UV Filter that comes with the Phantom 3. I have only tested this on a P3P and P3A. I do not have access to a P3S nor a P4 so I can't guarantee it will fit.
You MAY print as many as you need for your own use.
You may NOT make these to sell/trade/barter (either the printed part nor the model files).
You may NOT make derivative objects from these models for any reason.
The bezel is dimensioned to hold the larger filter size that
CG sells. I also included a stepdown inset in it that will hold the smaller size CP polarizers that he is currently shipping (what I got with mine anyway). So it will accept the smaller filter in the inset and the larger filter on top of that. For the inset to print properly you need a very fine print resolution of .15mm due to the thinness of the inset. If you do not have any of the smaller diameter filters, you can print it at .2, .3 or even .4mm layer height for much more rapid printing. Using the fine layer and my print settings, my Taz5 prints one in under 20min. With a layer height of .3mm print time drops to 10min.
When printed it should weigh approximately 2g.