https://usermanuals.finalemusic.com/FinaleWin/Content/Finale/Cross_staff_notes.htm 

In your example, you are probably best doing the notes manually rather than using the plug-in, which works better for contiguous notes. Let us know if you have follow-up questions.

Thanks Adrian. I was aware of the part of the manual you quoted but handled it incorrectly, it works now! Main problem is I'm used to work with a different music notation program which is limited but has a very intuitive UI.

See http://www.finalemusic.com/blog/finale-quicktips-cross-staff-beaming/

@Dean Crocker: thanks for your reply. I'm having a problem with the suggested solution, though. In my example (picture in my first comment) I would then have to select more than one single notes with the selection tool. However, if I click anywhere in the stave (Selection tool ON) the whole stave gets selected, if I click on an single note head, the SHIFT+ALT+Up/Down arrow doesn't work. What am I doing wrong?

Following my last comment: I succeed in selecting one single note. Is it possible in Finale to select more than one NOT ADJOINING notes? Thanks!

Is it possible in Finale to select more than one NOT ADJOINING notes?

As Far As I Know, non-contiguous selection of music is not (yet) possible in Finale.

@Peter Thomsen: thanks for your reply. Ok. I must say that I'm surprised that such an obvious feature is not possible in Finale. It will have a time consuming effect on many actions.

If it were me, I would do it like this. (Sorry for the huge grapic, but this "support" board apparently won't let you post Finale files!)

@Dean Crocker: Thank you for elaborating. Your method works fine for me up to stage 4. I discovered the 'Blank Notation: Layer 1' menu item but how do I copy? I don't see a 'copy' item and Ctr+C and Crt+V (Windows) don't seem to do anything.
And one more questions if I may: Is there a way to 'glue' the beams together from 2x4 to 1x8? Thanks!

More detail: :-)

5a. Click icon for SELECTION TOOL (That's the arrow up left)
b. Make sure Edit | Use Filter has a check mark next to it.
c. Edit | Edit Filter - click "All" then "OK".
d. Click and drag to select the first measure, both staves.
e. Edit | Copy (or CTRL-c)
f. Select 2nd measure, top staff.
g. Edit | Paste multiple | Paste Horizontally x times (however many bars the pattern goes on) | OK

To connect beams, you can use Utilities | Rebeam | Rebeam to time signature, setting the "imaginary" time signature to 1/2 instead of 2/4, for example.

@Dean - Thanks a lot, all worked fine!