You can do this now - whoever has the mission should enter USSs and look for the target - you and other friends should be following them in Supercruise. If there's no target, have your friend come back to SC and follow to the next USS.
Each time the person with the mission leaves Supercruise, they'll leave behind a Low Energy FSD Wake. If you target that and treat it like a station (close to within 1m/m and under 1000km/s), you can drop out of SC and follow the person into the USS. So, wait for them to confirm if the target is within the USS, then target their Wake, follow them in, and it's party-time/a seriously bad day for that Anaconda
It's important to note that right now, only the person who accepted the mission recieves the payout, so if you want to share the kill reward, the person who got paid will need to buy goods with a sell value equal to the other's desired payout, jettison them for the friends to pick up, and those friends will need to sell the goods on the black market (they'll be considered stolen) to make the cash. This is a pain in the butt, and there's talk the Wings update will allow you to actually split the bounty/reward on kill. I haven't been able confirm this from a Dev though.
My suggestion, if you're going to try this prior to the Wings update, just have everyone in the group find and accept a kill mission, and they all help each other complete each one. Much less messy on the back-end than the "goods as payment" option above.
