of course it can be done

so dont expect that any one will tell ya that it cant.
but its not the easiest work to do.. ill explain how it works (tho i doubt if you dont know).
when you do !search RLS\TOPIC or what ever it sends it to the host, if you use topic you should just run some search on your thread table, in title row, to check for matches, if it exists then it will send it back to the channel as notice, or to the user who requested it in pm (mostly there will be more then one result).
lets say you asked for the word "Crazy" and he found 5 threads, so from each thread you need to take (or in that case that what i would do) postusername, threadid, title. and i would make the output this way - Title: [bla] Crazy [/Bla] Poster: Mickey URL: http...threadid.

if you know some one who knows how to code tcl, it can make your life easier, cause you can grab some hack that already been posted here, and modify it for your needs
hope i helped you out to understand how it works if you didnt know, and if some one wants to code it, hope i guided him in some way
Greetz,
IM