Not as a direct feature (afaict - you aren't able to use the Edit>Shapes options to do a union for example), but the workaround is to create a new shape from one of the cells and stretch it to overlay the top two of the table, then group. This has some flaws in that when you resize the table to add more rows or columns, the overlaid shape does not stay associated with the top row or leftmost column - see this
film (~2MB, non-streaming)