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Well, I just tried it, and it worked, but it was finicky.
Master flash (an SB910, but should be the same as 900, on the TT1) set to commander mode. On the SB910 menu, I set the local flash to TTL, and channels A and B to manual.
Remote flashes on TT5's in TTL mode. Each TT5 set to A or B channel.
Now, here's the weird part. After a few presses, the test button on the TT1 would fire all 3 flashes as expected. But, after doing that, and taking a frame- no dice. Nothing flashed. So, I let the camera sleep. And then hit the shutter again, without hitting the test button, and the 2nd shot and those thereafter all worked OK.
I've never actually used this in practice. Here's what I do... and maybe it seems like a silly use of a PW but..... I put the TT1 or TT5 on my camera, and then go ahead and use my AC3 controller. It's SOOO much easier than the menu system in the 900/910. Then, I have a bracket (one of the ones that just goes to the side, custom brackets mini rc) with a TT5 and my "local" flash on it. So yeah..... I use a PW to trigger a flash that's mounted to my camera on a bracket, inches away from the transmitter. But I have extra PW's anyway, and it lets me use the AC3.