Threads Counting

[texasasl]

Due to huge of no use old threads I want to delete them but the problem is I do not want to modify the members' thread counter. That means in case I am deleting these threads the members' posts counter will be reduced dramatically. As of that I am searching a hack that will enable me to delete these threads which are just consuming a part of the database, without affecting the posts' countinging of the members.
I will be really appreciated if somebody can tell me how I will do this.