Yes, you are right, it is not very good for SEO
and we are aware of it and in upcoming version 5.0 there will be a native support for this.
Anyway, regarding this blog post comment
from our CTO Martin Hejtmanek - the very long comment, posted on 4/3/2009 2:01:02 AM):
<add key="CMSUsePermanentRedirect" value="true" /> which allows 301 redirection in places where it makes sense, instead of 302 redirection.
<add key="CMSRedirectAliasesToMainURL" value="true" /> which you can use for better SEO. It does 301 on every URL which is not main for the document (NodeAliasPath). That should help you for now.
<add key="CMSRedirectInvalidCasePages" value="true" /> which goes even further and allows you to restrict the pages only to a specific case variant. When the case is not right, it gets 301 to the right case.
So you can try to use these keys in the web.config file. I hope it will help.