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You have to estimate it based upon real world data at this point.

If you assume 90% VE at the point on the dyno where the torque curve is highest, e.g.

150 ft-lbs at highest peaks is 90% then (VEmax*0.9=150)
VEmax=167ft-lbs
then say you start at 2000 rpm with 125ft-lbs, you would have 125/167= ~0.75 or 75%
Then you can hand plot your estimate of VE based upon your torque curve. Of course diff. mods react diff. But if you get a car that was essentially the same with only a cam change we'll say, you can see how and where VE was effected by the cams.
Or an intake, headers, etc.