If you use DHCP, you can add the following to your dhcpd.conf file:
option option-143 code 143 = string; # (only for ISC's dhcpd v3)
option option-143 "9000";
Then restart your DHCP daemon. This is usually either
/etc/init.d/dhcp restart
or
/etc/init.d/dhcpd restart
If you use a local.cfg file, you can add the following to that file:
FLAMETHROWER_DIRECTORY_PORTBASE=9000