The text of the Executive Order is here:
http://www.cia.gov/cia/information/eo12333.html
You're right in that the assassination provision does not mention foreign government leaders.
"2.11 Prohibition on Assassination. No person employed by or acting on behalf of the United States Government shall engage in, or conspire to engage in, assassination."
If you look at the date of this EO some of you may be surpised! Dec 4, 1981.
This link includes the name of the signatory president at the bottom of the page:
http://www.fas.org/irp/offdocs/eo12333.htm
This gets more interesting all the time.
How hard would it be for Dubya to sign an order reading as follows:
"The provisions of EO 12333 Section 2.1 are suspended with respect to the following named individuals..."