That is doable, we have the data on hand inside the calculator. Would you want to see it under the 'More...' box? That is probably the best place to put it from a usability perspective.
Would it be helpful to see the pre boil gravity in the brew session section as well?
One thing to keep in mind is, the boil volume entered on the calculator, and the boil volume the brew feature computes can be slightly different. That is because the brew feature takes into account your equipment profile and works backwards from the batch size to arrive at the boil volume (since the boil off is based off your equipment, and everyone's is different).