It seems basepoint is the AutoCAD term for what we would call reference point or a point to snap from. Another alternative to the fence option which works just as well is Ninja-snapping which you use as follows.
- Select the elements you want to copy using Element Selection
- Place a manual snap/tentative point (not autosnap!) at the desired 'basepoint' position (bottom left of sheet etc..)
- Edit Menu/Copy
- Open up your destination DGN/model.
- Edit Menu Paste (you will see now the elements are not using the centre of their vertices range but instead use the 'basepoint'.
- Snap (manual or Autosnap) to the destination 'basepoint'
- Left click to place the copy in the model.