As akward and small as that space is, I can't think of a way to get at it without pulling the radiator. It is possible that you could go in from above after you have removed the shround, blade and clutch. You would need to do that if you end up pulling the radiator any way. If you end up pulling it I strongly suggest that you get it cleaned up and flow tested before you put it back in.
From what I recall from just flushing my cooling system. Once you remove the "guard" (4 bolts) just below the radiator, you have pretty good access to the drain plug. Since it is plastic, be extremely careful with an easy out and it should work.
Well.... This time I was prepared, I new the drain plug was not threading right and had a Toyota drain plug on hand. NOT.
I ended up pulling the rad as I had to drill out the old plug. Went ti install the new Toyota plug and guess WHAT #$%$#% the rad is a aftermarket and the OEM plug doesn't fit :'( I jumped in the semi with the rad and was lucky to find a FORD plug fits. 8)
It was a good thing I removed the rad, it gave me room to get a vice grip on the bolt as the torx part of the bolt striped. I would of had to remove the rad to get it off any ways.
I would say I am lucky, the BIG storm hit just seconds after I filled the rad with water 8)