[OpenAFS] a noobs question and problems on a new cell

[Adnoh]

hello @all
maybe stupid question but I don't know it :-)

i have two fileservers connected over a 2 mbit vpn (fs1 with rw-volume 
and fs2 with a ro-instance) and mounted that on /afs/domain/vol
can I settup this that way:
my users on fs1 work with /afs/domain/vol - rw + ro - thats clear to me.
when my users on fs2 read a file it should be taken from the ro-instance 
on the internal harddrive and if they change anything it is written to 
fs1-rw-instance !?
on my try i get only the error "readonly filesystem"

can this be done or do i have to setup a mountpoint /afs/domain/.vol 
(-rw) and point the users to that directory !?

thanks for any responses to help me getting started