[Evolution] Evolution 3.2.2: editing google calender of someone else?

[Joost Kraaijeveld <J Kraaijeveld Askesis nl>]

Hi,

I do not have a Google account but I want to edit the calendar of a
co-worker using Evolution. I can see his calender using his private ics
link. He has set the permissions for my e-mail address to "make changes
and manage sharing". I can see and open the events on his calendar but I
cannot edit the events: Evolution says: 
Event cannot be edited, because the selected calendar is read only.

Is it possible to do what I want or do I have to have a Google account? 
If it is possible, how? Any pointers to recent docs?

TIA

-- 
Groeten,

Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
web: www.askesis.nl