How to group whole notes/semibreves in one system?

[Klaus Föhl]

Hello,

One staff line with tenor and bass voices, discerned by stem direction.
Now there comes a whole note/semibreve and the bass splits into bass one
and bass two. How to show the middle note is bass one and not tenor two?

\arpeggioBracket <d a>\arpeggio 

looks about right visually to group the two bass voices save that the bracket
should be after the notes and not in front of them. How to achieve that?

Cheers
Klaus