Can the CI-V control outlet on the rear be used as a PTT outlet to control a MFJ-1708 SDR switch?

Could you use the send signal from the radio that would key a linear to control the SDR switch?
It might work quicker than the C-IV.

Where is the port for the send signal to the linear on the rear of the IC7000?

If I remember correctly it is on one of the DIN plugs ACCY 13 pin plug pin 3 (HF)(Page 12 of your manual) . Page 21 of your manual shows the hook up to a non-ICOM linear amp. You may need an external relay. If switching logic level you should be OK.