Run an extra push rod from the other side of the existing rudder servo. Hook that up to a tail wheel that includes a tiller type steering assembly. The sullivan tail wheels dont' work on an LT-40 unless you modify rudder (or the way the tail weel connects to the rudder). Something like this works:
http://www3.towerhobbies.com/cgi-bin...?&I=LXHDJ3&P=7
or this...
http://www3.towerhobbies.com/cgi-bin...?&I=LXD850&P=7
Here is how I did it:
http://www.rcuniverse.com/forum/m_19...tm.htm#1963113