Compile and install in non-standard directory

I expected this to be straightforward but I'm running into perplexing
problems and having little luck googling solutions. I would like to
install all of the compiled files in non-standard directories so I can
have the compiled version side-by-side with my current version. This
is with the PHP-5.6 branch from github, if relevant.

I'm running ./configure specifying both --prefix and --exec-prefix.
Compilation finishes without issue. The first thing I notice when I
run make install is it tries to dump the apache module in Apache's
default directory completely ignoring the specified prefixes. After
reviewing ./configure --help and all the documentation I can track
down, I don't see any clear solution to this. Is there a way to
specify an install path here that I'm missing?

Next I tried using INSTALL_PATH. This isn't ideal since it appear to
create /usr/lib etc directory levels under INSTALL_PATH, but at least
the setting works. Except this crashes too. I'm seeing this exact bug
from 2002 (reported as fixed but does not seem to be...):
https://bugs.php.net/bug.php?id=17491

If I run:
INSTALL_PATH=/home/andy/php56/ make install
The process dies with this error:
apxs:Error: Config file /home/andy/php56//etc/httpd/conf/httpd.conf not found.

I really don't need the install process monkeying with my Apache
configuration; I'm perfectly capable of adjusting it myself later. Is
there any option I can specify to simply make it skip that step? Again
I looked at the configure --help options and nothing stood out as
particularly likely.