Running for a VERY short time with no coolant?

[jof]

So the ally radiator's coming out this afternoon to trace a leak. If, as I suspect, there's a split my neighbour has kindly offered to take it in to work to get it welded properly (if I can't solder it)

Ideally I want it back in the garage tonight which is up a fair hill meaning it's not able to be pushed

What's the view in running the engine for 20 or 30 seconds with no coolant in the system at all?