Cross-voice arpeggios

[Bertalan Fodor]

I want to make cross-voice arpeggios for 2.2.5

I've found this but, \hideNotes in not allowed chords:
http://lists.gnu.org/archive/html/lilypond-user/2003-10/msg00032.html

So I invented a solution:
<<  \context Voice = "arp" { \hideNotes <cis' e,>4.\arpeggio }
{ cis4. h8 a4} \\ { <gis e>2 fis4 }
>>
I.e. I use an invisible chord for making the arpeggio.
But that gives me a warning about clashing notecolumns (I understand 
why), and I'm curious if there is a cleaner solution. Does anyone have 
something like this?

Bert