Teaching Relaxation

Most sprinters come from a football or soccer background where they usually don’t run very relaxed. They push with all of the intensity they have to get to the ball or to “light” some guy up. Therefore, when you teach them to relax in sprinting it is a fairly difficult and sometime ardous process, but you don’t have to worry about them going anything but maximum effort.

My question is: How do you teach someone from a distance (XC) background to harness their intensity?

From day 1 a distance runner is taught to relax when they run (believe me you may not notice how tired you are after 60m tight, but 3miles tight really sucks) and it just comes naturally that they waste little energy in tightness when the sprint. However, I have the problem of getting real intense and harnessing as much of my muscle power while staying relaxed, I either flip (and go too hard) or flop (and go too easy). I notice i don’t have this problem when I go into my kick phase in the 800 I simply speed up and dust the other runner, but my 400 time hasn’t improved much at all and I feel that I’m not reaching my “real” 400 pace because I’m “too” relaxed. (in comparison with a total of 10 seconds worth of pr’ing in the 800)

Are there any mental or visual cues that i should do to help me really attack the track?