11-13-2018 09:11 AM - edited 11-13-2018 09:14 AM
I just tested the TC-80N3 with my 1DX 2. With the camera set to high speed continuous and the TC-80N3 set to long exposure mode it will count down to start and then the 1DX 2 fires in high speed mode until the long exposure period times out. So it would do what you need with the 1DX 2 but I don't know if your 7D 2 will behave in a similar manner.
Note for this test I had the TC-80N3 set to stack its self timer and long exposure modes so after you press the start button on the remote it counts down the self timer delay and then starts the long exposure series of shots sequence.
11-13-2018 12:31 PM
You are welcome. I am not 100% sure it would work the same on the 7D but I am pretty confident it would. I also tried it on my 1DX (non Mark II) model and it works the same with it in providing a series of shots. Effectively it is doing the equivalent of holding the shutter release electronically when in long exposure mode so with the camera set to continuous it will keep shooting.
You can find a used one on Ebay for a lot less than new, they are a very common accessory that has been around for a long time. I bought mine back in 2005 from B&H at the same time I ordered my 1D Mark II.