In theory, it should be easy. You just add an entry to /usr/lib/tztab and set your TZ environment variable to the new entry. If there is no switch into daylight savings time, you do not need any entry in tztab. And the is a "man tztab" to guide you.

But you need to know when the daylight savings shift occurs. That is a real problem with Israel. See this page for details. Edit: Here is a file with an entry for 1992-2038. If you go up one level from here you will see an INSTALL file which you should ignore. It is for HP-UX 9.x and it is not a very good procedure even for that OS.