This works for me:
sudo -s
Download source
mkdir /usr/local/src/php5-build
cd /usr/local/src/php5-build
wget -O php-5.3.29.tar.gz http://de1.php.net/get/php-5.3.29.tar.gz/from/this/mirror
tar -xzf php-5.3.29.tar.gz
cd php-5.3.29
Install all necessary dependencies
apt-get install apache2 php5 php5-common php5-cli php5-mysql php5-gd php5-mcrypt php5-curl libapache2-mod-php5 php5-xmlrpc mysql-server mysql-client libapache2-mod-fastcgi
apt-get install build-essential php5-dev libbz2-dev libmysqlclient-dev libxpm-dev libmcrypt-dev libcurl4-gnutls-dev libxml2-dev libjpeg-dev libpng12-dev
Compile PHP
./configure --prefix=/usr/share/php53 --datadir=/usr/share/php53 --mandir=/usr/share/man --bindir=/usr/bin/php53 --includedir=/usr/include/php53 --sysconfdir=/etc/php53/apache2 --with-config-file-path=/etc/php53/apache2 --with-config-file-scan-dir=/etc/php53/conf.d --enable-bcmath --with-curl=shared,/usr --with-mcrypt=shared,/usr --enable-cli --with-gd --with-mysql --with-mysqli --enable-libxml --enable-session --enable-xml --enable-simplexml --enable-filter --enable-inline-optimization --with-jpeg-dir --with-png-dir --with-zlib --with-bz2 --with-curl --enable-exif --enable-soap --with-pic --disable-rpath --disable-static --enable-shared --with-gnu-ld --enable-mbstring
make && make install
Activate Apache module
a2enmod cgi fastcgi actions
service apache2 restart
Create corresponding configuration file
vi /etc/apache2/php53.conf
Insert:
#Include file for virtual hosts that need to run PHP 5.3
SetHandler application/x-httpd-php5
ScriptAlias /php53-cgi /usr/lib/cgi-bin/php53-cgi
Action application/x-httpd-php5 /php53-cgi
AddHandler application/x-httpd-php5 .php
Create environment script to start the additional PHP version
vi /usr/lib/cgi-bin/php53-cgi
Insert:
#!/bin/sh
PHPRC="/etc/php53/apache2/"
export PHPRC
PHP_FCGI_CHILDREN=4
export PHP_FCGI_CHILDREN
PHP_FCGI_MAX_REQUESTS=5000
export PHP_FCGI_MAX_REQUESTS
exec /usr/bin/php53/php-cgi
Configure Apache 2's virtual hosts
Include php53.conf
ServerName example.org
DocumentRoot /var/www/sites/example.org
Options Indexes FollowSymLinks MultiViews
AllowOverride all
Require all granted
Last, restart...
service apache2 restart
Source: https://erdfisch.de/en/multiple-versions-php-apache-under-linux