IP Header has a length of 24 bytes

Previous (unanswered) question has similar problem to me so I thought I’d repost (with higher points !!)-

IP Header has a length of 24 Bytes
a Cisco router sends an UDP request, the length of its IP-header is strictly 20 bytes, to a windows2000server.
Within the UDP answer,my windows2000 server sends an IP-header with a length of 24 bytes
because it adds 4 bytes for “options = no options” to the router.
therefor my firewall rejects this answer because of a security lack.
now my question:where / how can I configure the TCP/IP options in that way, that my header will not exceed a length of 20 bytes.