It is true, we'd be asking Maguire to cover about 150 yards. The thing it would do is mean the opposition leave 2 back, but most leave 1 anyway with another 25-30 yards from goal. Leaving 3 up every now and then would cause confusion and would be worth trying every now and then.
When we're under pressure and defending a corner the key thing from it is to not concede, not to try and get a goal from the counter. More players around the 25-30 yard mark would make more sense then someone stood isolated on the half way line.