Jeff,
It is possible, but note that that is just a first step. Then you'll need to adjust the DAL (Data Access Layer) to reflect those changes. I.e. Sql SPROCS, DataProvider and SqlDataProvider, and ObjectsBLL. Finally you will need to change the UI.
About the sorting: Did you use the SortExpression field in the column list yet? This is position 6 in the array of the column parameters. Your column would be something like:
CustAtt1|My Custom Attribute|||||CustAtt1||||
The first 'CustAtt1' is the reference for the value it is to display, the second is on what it should sort. The idea is that this would allow the column to sort.
Peter