I may not know how to do but it’s probably a valuable new feature. During a free-ride I joined a pace partner and decided to ride with the group. At every junction it’s necessary to select appropriate exit. So my requested feature is a ‘keep riding with the PP’ button. Makes sense?
I’d absolutely love this feature and think about it every time I’m riding past a pace-partner.
I’d especially like to be able to start with, say, the 1.8W/kg partner and hop onto the 2.2W/kg without having to exit my ride and start over.
I suspect, however, this is a software limitation - Zwift’s code-base probably prevents both of the above from being made possible.
I rather expect no limitations. During a ride you’re transferred to events, even to different worlds. Well, this takes time but it’s exactly the same to hop onto a new PP. To stay w/ a PP would not even require a change of world but probably a toggled flag only … junction_card = ‘invisible’ … and a pre-defined junction_option = junction_option(active PP) instead of the defaulted selection currently displayed.
It’s not ideal but it is possible, with a little research.
For example, this week Coco has been on one of my favourite routes - Three Little Sisters. But i wanted a few minutes warm up to get the legs going before getting in to the rollers of Titan’s or climbing the Volcano.
So i selected the same route and started to free ride… Now if you are lucky you could end up on the route and have the pacer group sweep you up once warmed up. Dandy. However you might also find that they are over the other side of the route and you have to search for them… So use the ‘search zwifters’ function on your companion app combined with the ‘fan view’ to see where they are.
You can then use manual turns to intercept the pacer group. Now remember that once you return to the route you originally selected the system will auto turn so you should follow the pacer group.
One draw back… some pacer routes can’t be selected from the route list.
Are you sure? I don‘t think you are back on track. As soon as you do one manual turn, you are off course/route and only Zwift knows where you are heading. Maybe even Zwift don‘t know it? 
Yes… If you select a route and manual turn off of it you obviously follow a random auto turn dictated by Zwift. However, if you return to the route you were previously on (& correct direction), the auto turn will again follow your originally selected route.
I do this quite regularly to mix up my rides.
I agree, although to be clear I think it has to be the original route that you chose from the main menu for your workout. I was playing around with this in London the other day. If you change routes and ride what you know is a second route via manual turns, and then try a third, if you go back to the second you would still have to manually turn. But going back to the first route/direction puts you back on the original route with autoturns.
Lots of previous requests for this feature. Below is just a sample. I think @James_Zwift said this is being considered but I didn’t find his comment.