The folks at MyDutchBike sold me the bobike, gave me some info, and pointed me towards this helpful flickr page for ideas. In order to make room for two bobikes or to use the bakfiets seatbelts, one side of the bobike needs to be shaved off, along with the metal leg posts. Since I only have one kid for now, and I was pretty sure I couldn't cut the edge off without making it all ragged, I decided on a different method. After staring at it for quite awhile, I decided I could use a 1" wide rachet tie-down strap to attach the bobike to the bakfiets seat.
I tested it out and it worked great, but the problem was that the only point of attachment is the two little seat pivots, which don't look like they would hold much. So I decided to drill two additional holes and move one of the seatbelts to the center.
Here is the left seatbelt removed with two holes drilled in the center.
Left seatbelt migrated to the center.
The slightly tricky part is using the ratchet tie down to attach the bobike to the bench. The tie down passes through two slits at the back of the bobike, and around the metal bars in the front. The bobike comes with it's own seatbelt, but I cut it off, leaving just the rigid crotch strap.
This is the rachet attachment underneath the seat. The seat is short, so I had to hook the ratchet to itself in the shortest possible configuration.
And here's the finished product. The bobike is still only attached to the bench. But with a kid buckled in, the seatbelt adds an attachment to the bucket.
Since I already have two eyebolts installed for the infant seat, just to be extra anal about safety, I added two quickdraws, so even if the bench totally fails, the bobike isn't going anywhere.
We did a little dry run in front of the house and Silas seems to love being able to see where we're going.