OS : CentOS 5.10 and CentOS 6.5
Plesk Versions : 11 and 11.5
Preparation: Install required components
From PPP, install the app template "devel"
yum groupinstall "Development tools"
yum install libjpeg-devel libc-client-devel libicu-devel libmcrypt-devel.x86_64 unixODBC-devel postgresql-devel aspell-devel libtool-ltdl-devel gmp-devel openldap-devel net-snmp-devel libxslt-devel
Compile and install PHP. This article is using PHP verison 5.4.30 as example.
1. Login to VPS via SSH
2. Download and extract the php source files. Use wget to download the php source gzip file. Check the version in the link
cd /tmp
wget http://hk1.php.net/distributions/php-5.4.30.tar.gz
tar zxf php-5.4.30.tar.gz
cd php-5.4.30/
3. Configure and compile PHP
./configure '--with-libdir=lib64' '--cache-file=../config.cache' '--prefix=/usr/local/php540-cgi' '--with-config-file-path=/usr/local/php540-cgi/etc' '--disable-debug' '--with-pic' '--disable-rpath' '--with-bz2' '--with-curl' '--with-freetype-dir=/usr/local/php540-cgi' '--with-png-dir=/usr/local/php540-cgi' '--enable-gd-native-ttf' '--without-gdbm' '--with-gettext' '--with-gmp' '--with-iconv' '--with-jpeg-dir=/usr/local/php540-cgi' '--with-openssl' '--with-pspell' '--with-pcre-regex' '--with-zlib' '--enable-exif' '--enable-ftp' '--enable-sockets' '--enable-sysvsem' '--enable-sysvshm' '--enable-sysvmsg' '--enable-wddx' '--with-kerberos' '--with-unixODBC=/usr' '--enable-shmop' '--enable-calendar' '--without-sqlite3' '--with-libxml-dir=/usr/local/php540-cgi' '--enable-pcntl' '--with-imap' '--with-imap-ssl' '--enable-mbstring' '--enable-mbregex' '--with-gd' '--enable-bcmath' '--with-xmlrpc' '--with-ldap' '--with-ldap-sasl' '--with-mysql=/usr' '--with-mysqli' '--with-snmp' '--enable-soap' '--with-xsl' '--enable-xmlreader' '--enable-xmlwriter' '--enable-pdo' '--with-pdo-mysql' '--with-pdo-pgsql' '--with-pear=/usr/local/php540-cgi/pear' '--with-mcrypt' '--enable-intl' '--without-pdo-sqlite' '--with-config-file-scan-dir=/usr/local/php540-cgi/php.d'
make
make install
4. Copy the php.ini file
cp /etc/php.ini /usr/local/php540-cgi/etc/php.ini
5. Register new PHP under Plesk
/usr/local/psa/bin/php_handler --add -displayname 5.4.30-custom -path /usr/local/php540-cgi/bin/php-cgi -phpini /usr/local/php540-cgi/etc/php.ini -type cgi -id 5.4.30-custom
Select New Installed PHP under Plesk Panel:
1. Goto Hosting Settings
2. Select : PHP support (Run PHP as "CGI Appliction" , PHP version "5.4.30-custom" )

Source:
http://download1.parallels.com/Plesk/Doc/en-US/online/plesk-administrator-guide/index.htm?fileName=72042.htm
http://kb.parallels.com/114753
http://kb.parallels.com/en/118378