How about this (ker-lunk!)

declare @dbname as varchar(100)

declare @strSQL as varchar(100)

declare @strSQLCommand as varchar(100)

set @strSQLCommand='exec sp_adduser ''Victoria'', ''Victoria'', ''db_owner'''

set @dbname='Whatever'

-- your db loop here

set @strsql='USE ' + @dbName + '; ' + @strSQLCommand + ';'

exec(@strSQL)