question on Apache2_4::AuthCookie

Hi.
I have (a long time ago) created an AAA module based originally on Apache2::AuthCookie (a 
copy and rewrite, not a sub-class). Now I need to adapt this to Apache 2.4.
I have read all the docs at 
https://metacpan.org/source/MSCHOUT/Apache-AuthCookie-3.24/lib/Apache2_4/AuthCookie.pm, 
and followed the related correspondence on this list.
My problem is that I would like to keep a single perl source, for both Apache 2.2 and 
Apache 2.4.
As far as I can tell so far, this should not be a big problem, except for the following 
difference :

In the Apache 2.2 version, I have this statement :

use Apache2::Const -compile => qw(:common :http :methods :override :proxy);

and in the Apache 2.4 version, I must have this statement or it will not compile :

use Apache2::Const -compile => qw(:common :http :methods :override :proxy AUTHZ_GRANTED 
AUTHZ_DENIED AUTHZ_DENIED_NO_USER);

(That is because these new AUTHZ_* constants must be used in the new "AuthzProvider" subs).

I could of course hack the values of these constants under 2.4, and use their values 
directly in my module, but that is rather "inelegant".

My question is thus : would there be a way to make the import of these constants 
conditional on the Apache version the module is running under ?
(In other words e.g. define them with value 0 initially (for Apache 2.2, since they are 
never used there), and override them if under Apache 2.4 ?

Or, to put this another way : imagining that there are already some servers, currently 
running Apache 2.2 with, say, mod_perl 2.0.7, and on which the current (2.2-only) version 
of my Auth module is running.
If I ever update these servers with the latest (2.4-compatible) version of my module, 
including the above extra imported constants, that updated module will not compile anymore 
on those systems (because these constants are not defined there).
Is there a way to avoid this incompatibility ?

I tried to phrase the above as clearly as possible, but if it is still confusing, I can 
try again..

Thanks