There is a package for amd64
http://snapshot.debian.org/archive/debian/20110406T213352Z/pool/main/o/openssl098/libssl0.9.8_0.9.8o-7_amd64.deb
and then install it:
root@07:/etc/php5/fpm/conf.d# dpkg -i libssl0.9.8_0.9.8o-7_amd64.deb
Selecting previously unselected package libssl0.9.8.
(Reading database ... 120511 files and directories currently installed.)
Unpacking libssl0.9.8 (from libssl0.9.8_0.9.8o-7_amd64.deb) ...
Setting up libssl0.9.8 (0.9.8o-7) ...
root@07:/etc/php5/fpm/conf.d# php -v
PHP 5.4.4-14+deb7u2 (cli) (built: Jun 5 2013 07:56:44)
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2012 Zend Technologies
with Xdebug v2.2.1, Copyright (c) 2002-2012, by Derick Rethans
with Zend Debugger v5.3, Copyright (c) 1999-2010, by Zend Technologies
root@07:/etc/php5/fpm/conf.d#