For $4.95 get a MiniMagLite Accessory kit (available at BrightGuy.com and others, even places like Campmor.com & REI.com).
The clip can be spread sufficiently AS it goes over the head of the P1D-CE. I know, as i have one in my left front pocket right now with the said clip on it.
The clip also fits other Fenix models (AA and CR123A). On some flashlights, it's easier to slip it onto the thinner part of the body and then force slide it up to the location where you really want it.
In one case (yeah,...i've bought several minimaglite accessory kits over the last year or so), i needed to pre-spread the clip just a bit before attempting to get it onto the flashlight.
In the case of the P1D-CE, it's easier to select your mode before clipping it to a cap brim/visor for hands-free use.
Obviously, the clip works well for afixing the P1D-CE to a shirt or pant pocket or a backpack strap, etc.
The clip from a older CMG/Gerber Infinity task light is also an option which i've used (haven't tried the newer Infinity clips).
You might also find an el-cheapo AA flashlight somewhere (Walmart???) with a removable clip on it that you could conscript into service on your Fenix.