Something that strikes me is how early on in the investigation the bin lorry was identified. I'm inclined to think there was a reason for this, and I do think it is likely that Corrie's phone was in it, though he was not.
So here's one potential scenario which both accommodates that and explains how Corrie might have come to leave the horseshoe area in a vehicle.
Corrie enters the horseshoe area with the intention of having a pee. Already in the area is a parked car and driver. Corrie puts his phone on top of the bin whilst he has a pee. As soon as he has finished, the driver of the car attracts his attention for some purpose; lecturing him on urinating in public/ asking for directions / whatever. They get into a conversation.
The bin lorry arrives whilst they are talking, and takes Corrie's phone away with the bin. He realises what has happened almost immediately, but too late to stop it.
At this point, the driver of the car tells him to hop in; they'll follow the lorry and flag it down. Corrie may even have made the suggestion himself.
From here, there are a number of possibilities:
1) Corrie had the tremendous misfortune to have stumbled upon someone with pre-existing criminal intentions, who took opportunistic advantage of the situation to abduct and kill him. This would be a tremendous coincidence, but it's not impossible.
2) there was no initial malicious intention on the part of the driver, but there was an argument en route; perhaps Corrie was sick in the car, and was ejected, possibly forcibly. This could have happened in the middle of nowhere; Corrie tried to make his way back on foot but met with an accident and has not been found. The driver hasn't come forward because they feel guilty about abandoning him, especially if physical force was involved.
3) nothing untoward took place involving the driver; he dropped Corrie off somewhere, perhaps after Corrie had decided that pursuing the bin lorry was a bit of a wild goose chase and he might as well write the phone off and go home. From here, it's the same scenario as in 2; Corrie met with an accident whilst walking home. The driver hasn't come forward, not for any reasons relating to Corrie, but because they don't want police attention on their activities in the earlier part of the night, for whatever reason.
The only slight snag to this theory is that the conversation between Corrie and the driver would have had to have been a fairly lengthy one, if the bin lorry didn't arrive until around 4am. But I'm not sure if we ever had that time definitely confirmed, did we? I think we know his phone was still pinging a mast in central BSE at 4am, but that would allow the bin lorry to have exited the horseshoe area somewhat earlier.