.PSECT  DATA,WRT,NOEXE,5
CTRL_C_AST:
        .LONG   3                               ; 3 arguments
        .ADDRESS your_ctrl_c_ast_routine        ; DCLAST$_ASTADR
        .LONG   0                               ; DCLAST$_ASTPRM
        .LONG   0                               ; DCLAST$_ACMODE


        .PSECT  CODE,NOWRT,EXE,5
        .ENTRY  some_name,0

        $CMEXEC_S       ROUTIN=SYS$DCLAST,-
                        ARGLST=CTRL_C_AST

        RET
        .END    


This will queue the AST for execution in EXECUTIVE mode.  You will
need CMEXEC privilege to test this out.  If this works, you'll need 
to implement a user written system service or install your program
with the CMEXEC privilege to allow this to function for the average
non-privileged user.

VAXman- A Bored Certified VMS Kernel Mode Hacker      VAXman(at)TMESIS(dot)COM