Jim,
Pardon me for my oversimplified suggestion, but couldn't you do something like this:

do case
case USED( JUSTSTEM( this.controlsource ) )
   * it's a cursor/table/view field
case VARTYPE( JUSTSTEM( this.controlsource )) = "O"
   * Object property
otherwise
   * it's a memory variable
endcase

Hope that helps (somewhat).