Put a asp:placeholder or asp:literal in masterpage. When you want to have a canonical-tag from an inheriting page, just give placeholder / literal value.

Thanks for your help René!

Yes, I mean GTW of course :).

A folder for each site would definitely make some things easier, but it would also mean more work every time we need to republish the site or make configurations.

Did I understand that googlelink correctly in that if we have verified ownership in GWT for all involved domains cross-site submission in robots.txt was okay? I guess google will think its okay anyway.

Thanks for your response René!

Thing is we already submit the sitemaps in google analytics, but this SEO company we hired wants us to put the sitemaps in robots.txt as well.

The .htaccess idea sounds good, as long as google or someone else dont think we are doing some cross-site submission error (as described here http://www.sitemaps.org/protocol.php#submit_robots)

we have www.mysite.net, www.mysite.se, www.mysite.fi and so on. all of these domains point to the same physical location on our webserver, and we replace texts given back to client depending on which domain he/she requested.

My problem is this: How do i configure sitemaps in robots.txt when robots.txt is used by multiple domains? If I for instance put the rows

Sitemap: http://www.mysite.net/sitemapNet.xml
Sitemap: http://www.mysite.net/sitemapSe.xml

in robots.txt, would that result in some cross submission error?