TT is about discipline. If your friend has none, a meter isn't going to help any.

I rode my first TT in about 1977. We got on a road bike and went 25 miles (not 40K) as fast as we could. We had speedometers that ran off the front wheel or your watch and a target time for the turnaround.

TT has always been matter of "pacing yourself" and instrumentation makes it easier, but probably makes people ride too conservatively also.