For any well appointed rowing club this is something that would not be hard to do (but might be frustrating in its details). I agree to post on this site the results of any serious attempt to fill this gap in the knowledge of rowing.
The determination of the mass of the (seated) shell alone is a matter of simple weighing of the boat, oars, and crew.
The determination of the added mass can be approached either theoretically or empirically.
A theoretical approach might involve the estimation of the average thickness of the bound layer from the laws of fluid dynamics for various hulls and multiplying those by the wetted surfaces and the fluid density. It might then be repeated for a range of hull speeds and boats to form a parametric function which could then be used in any model.
However, an empirical approach might enable the direct determination of the added mass by "weighing" the boat and its bound layer together by inertial means. I think this is relatively easily possible.
Suppose a (seated) shell to be set in motion in still water by the application of a known constant force (a falling weight?) and the resulting acceleration noted at various stages during the resulting speed increase. The net mass accelerated at each stage (including that of any bound layer) is then a matter of simple calculation (m=F/a); and that "added" the result of subtracting out the known dead weight of the (seated) hull.