I want to use Hot shoe flash + extra RF trigger

I want to mount a radio trigger on a camera bracket, the bracket will have hot shoe for the radio trigger with a cable to plug in to the camera PC sync. This will allow me to have the 600EX or ST-E3 on camera (hot shoe) and trigger manual set off camera lights via a different radio system.

Has anyone seen a similar rig?
Is the a PC sync to hot shoe cable? I haven't been able to find one.

A Pixel TF-321 will provide a hotshoe for your manual trigger that could be mounted on your bracket. It has a standard PC Sync connection on the side that could be used to connect to your camera PC sync jack via a short cable to provide a fire signal for a mounted manual trigger. It runs $12.95.
Here is a link: http://www.amazon.com …a-Flashguns/dp/B00554PCD​G

Do you already have the manual trigger system? If not, you could instead pick up a pair of Comtrig T-320 manual triggers for $32.69 that provide full TTL passthrough. That way you could mount the T-320 Tx on your camera hotshoe and the ST-E3 on top of the T-320. The ST-E3 would operate exactly like it does when mounted directly to the camera and the T-320 would fire your remote manual flash when you trip the shutter.
Here is a link to the T-320: http://www.amazon.com …1-1&keywords=comtrig+t32​0

I don't have an ST-E3 but I have tested this exact scenario with one 600EX-RT mounted on top of a T-320 firing a remote 600EX-RT in Group mode, with a YN-560II manual remote flash unit triggered by the T-320 system. The on camera 600EX-RT retains full two way communication with the camera in this configuration and I can even control the firing of the manual remote flash from the camera by simply switching the T-320 Tx on or off. The TTL passthrough is not dependent on the power status of the transmitter so the ST-E3/600EX will trigger either way. It is actually very simple in use and allows me to avoid notoriously failure prone PC sync cables. Just an option to consider.

I started out using this system:

A flash mounted on the top of the bracket and a pocket wizard on the flash bracket.

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I use a Phottix Stratos which has an E-TTL Pass Through Hot Shoe and is a 4 Channel Manual Trigger. Mine were bought from Calumet (their branding on them). Mount the Trigger in the Hot Shoe and the Flash onto the Trigger. Works well, little bulk.

CanonCameraFan wrote in post #16228545
I use a Phottix Stratos which has an E-TTL Pass Through Hot Shoe and is a 4 Channel Manual Trigger. Mine were bought from Calumet (their branding on them). Mount the Trigger in the Hot Shoe and the Flash onto the Trigger. Works well, little bulk.

^This. If you are not already invested in the RF trigger system, pick up the Strato II Multi and use the hot-shoe pass-thru for the 600EX-RT.