[GNC] Asset Allocation by Sector

[rsbrux]

I have been using GC for years for all of my bookkeeping, including investment tracking.
I have managed to make rudimentary Asset Allocation reports for the major investment types (stocks, bonds, funds, etc.) but would like to also monitor the distribution of my investments over sector (financial, industrial, pharmaceutical, etc.)
I don't find any way to do this in GC, or even a way to associate a given investment with a given sector.
How do other GC users handle this?  Is there some add-on or external tool anyone can recommend?