The solution is actually embarrassingly simple.
The cipher/protocol settings for how clients can connect to the reverse proxy do not effect how the reverse proxy negotiates a connection to a back-end server.
In other words, I was able to disable SSL and harden the cipher's on the reverse proxy and the reverse proxy was still able to use the weaker protocols to connect to the old back-end server.
For the curious, these are the settings I used in the /etc/apache2/mods-enabled/ssl.conf file on my Ubuntu 14.04 LTS server running Apache 2.4.7 to disable SSL and harden the cipher's used:
SSLProtocol all -SSLv3
# NOTE: Do not add -SSLv2 as some sites suggest (It's already not supported)