I soldered the pogo pins to one of the perfboards.

The typical ISP connector (6-pin male) I soldered to a second perfboard.

On the opposite side of the second perfboard I soldered the two 3pin pin headers. They do not have any electrical function. They just provide mechanical stability.

Then I soldered the ends of the pogo pins to the ends of the pins of the ISP connector (kind of a butt coupling).

Finally I soldered the stabilizing pin headers also to the first board and cut away a small piece of the board near the ISP connector to mark pin 1.