This probably needs to be

<code>rest_method "ADD_ENVIRONMENT_VARIABLE", :id => env_name, :value => env_value
</code>

or I get

<pre>
# rhc apps
/usr/lib/ruby/gems/1.8/gems/rhc-1.10.1/lib/rhc/rest/client.rb:463:in `parse_response': /usr/lib/ruby/gems/1.8/gems/rhc-1.10.1/lib/rhc/rest/application.rb:119: syntax error, unexpected ':', expecting kEND (SyntaxError)
...ADD_ENVIRONMENT_VARIABLE", id: env_name, value: env_value
                              ^
/usr/lib/ruby/gems/1.8/gems/rhc-1.10.1/lib/rhc/rest/application.rb:119: syntax error, unexpected ':', expecting '='
...ARIABLE", id: env_name, value: env_value
                              ^
</pre>