I think the last time R2 had one of their mainstream weekday presenters, sitting on for another mainstream weekday presenter was Johnny Walker sitting in for Wogan (about 15 years ago ?)
That did happen a few times, and then when Walker moved off drivetime in 2006, it was announced he'd be the regular stand-in for Wogan.
It happens much more frequently on Radio 1, Scott Mills was the regular stand-in for Nick Grimshaw, although it makes sense to have a high profile stand-in on the biggest show on the station. I remember during the short-lived period Mark and Lard were on breakfast, Kevin Greening was their stand-in, when he was doing drivetime, and in turn Mark Goodier would stand in for him on drivetime - which struck me as odd as Goodier was the previous presenter of that slot so he was standing in on his old show.
Indeed, will be interesting to see if Scott Mills continues to be Greg's cover on Breakfast. I think he's already done it a few times but they also had Matt and Mollie from weekend breakfast cover over the new year, which IMO makes more sense, especially since they now do Fridays so weekend breakfast is a better gig than it was before.
623058: it just seems like your an mp3 whore