Expanding GraphDefs is similar to edge expansion except you specify the criteria before you call the function to run the graph. This allows you to specify multiple OBIDs as the starting point for the graph.
Dim lobjGraph As IDirectedGraphDef = CType(lobjGraphRel.GetEnd1.ToInterface("IDirectedGraphDef"), IDirectedGraphDef)
Dim lobjQueryReq As SPFRequestContext.Instance.QueryRequest
lobjQueryReq.AddQueryGraphDefCriteria(lobjGraphRel.EdgeRole, "OBID", "", "IN(" & OBID & ")")
Dim lobjGraphResults As StructuredObjectCollection = lobjQueryReq.RunByExpandGraphDef(lobjGraph)
lobjIncludesObjects.AddRange(lobjGraphResults.AllObjects)