Considered spam..well..it is spam.. dont do it.The SE's will catch you..some take longer than others but about the time you start to get traffic ..all of a sudden you'll see your domins are not listed anymore..
Then there you are starting all over again..
Why not just add a link from 9 of the sites (as long as they are not mirror sites) to your "main" domain..
That will help your main domain much more than trying to "cheat" the engines..
Just be careful and dont start a link farm
http://www.netmechanic.com/news/vol5/promo_no7.htm