I had this problem when I changed mine a few years ago. To get the clip back on I got a tubular piece of wood about as long as the push rod, maybe slightly shorter. Something like a broom handle will do. I then drilled a hole through the centre of the wood so the pushrod wood fit through it. Then I put the clip on pushrod, put the pushrod into the wood so the clip is trapped against the end of the piece of wood and the bulbous end of the pushrod and carefully clipped it back onto the fork through the slave cylinder hole and slipped off the piece of wood.
Hope that makes sense!