That's the biggest waste of a roster space and the worst idea ever...
Why are people OBSESSED with the 40? It's the most overrated thing ever. As long as he's football/functional fast, then I don't care what his 40 is. Give me a guy who runs a 4.6 and can read a defense and run routes over someone like Goodwin or Troy WIlliamson. Jerry Rice, Anquan Boldin, Steve Largent, Cris Carter, Wes Welker, Michael Irvin, all "slow" WR's but some of the best to ever lace them up. Most importantly they'll outlast any "track guy" because they don't rely on athletic ability to get open.
And if they're going to run the 40 yd dash at the combine, put the dam pads on.