If you label the lamps like this:
1 4
2 5
3 6
Then one of the solutions is 23461 (I suppose any order of these switches works, really, but I find ending with 1 to be more dramatic). But try to solve this yourself to find out whether there is a shorter combination. You just need to note which switch on the lamp post affects which lamps.
Or you can cut the wires on the ground (or could in version 1.0.4 at least).