To insert a tsl from palette or ribbon you need to call the hsb_scriptinsert command with some arguments.
Create a command on the fly:
(defun c:NEWCOMMAND() (hsb_scriptinsert "TSLNAME" "CATALOGENTRY")) C:NEWCOMMAND
NEWCOMMAND: replace this by any command name you want to assign, but make sure you are not overwriting an existing hsbcad or Autocad command.
You could use one command name for multiple tsls if you do not want to call the command from command line, but just ensure to make a command repeatable, i.e. "MyLastTslCommand"
TSLNAME: replace this by the tsl name. Do not add a path if the tsl can be found in the root of hsbcad or hsbCompany
CATALOGENTRY: (optional) replace this by a catalog entry which you have stored of this tsl. If the catalog entry cannot be found the default will be used. TSL could support a silent insert without any dialog appearing if a valid entry name is given (if this has been envisaged by the author)