OPTIONS or IGNORE based on OSVERSION?

Hello,

I'm trying to give www/mod_auth_gssapi support for MIT Kerberos in base 
on FreeBSD 15+. That part is actually easy, but what I cannot figure out 
is how to treat earlier versions.

What I would like to do is either not offer the option at all or, if 
that is not possible, IGNORE if the GSSAPI_BASE option is set and the 
system does not have MIT Kerberos in base (OSVERSION < 1500054).

I tried wrapping the entire OPTIONS block in

	.if ${OPSYS} == FreeBSD && ${OSVERSION} < 1500054

, but that needs <bsd.port.options.mk> for OSVERSION, and that in turn 
must come _after_ the OPTIONS block. Using <bsd.port.pre.mk> instead 
does not work either; it breaks make config (or in my case, poudriere 
options), the options just aren't set anymore.

I also tried

	.if ${OPSYS} == FreeBSD && ${OSVERSION} < 1500054
	GSSAPI_BASE_IGNORE=	Needs MIT Kerberos in base
	.endif

, and that has the same problem: If it is after <bsd.port.options.mk> it 
does not work, and if it is before, I don't have OPSYS and/or OSVERSION.

Is there a way to do this, or perhaps a much better solution I have not 
thought of, and should I even spend more time working on it with 14.3 
going out of support in five months?

Thanks for any help.

-- 
Christian