[Puppet Users] Changing Agent Environment Via Custom Fact

It is very likely that I don't completely understand the order of
operations as they pertain to agent level variables (such as environment,)
but I'm not seeing where this should be a problem.

What I'm Trying To Do: Set environment on a host by setting a custom fact.

How I'm trying to achieve this: I have a custom module that parses ec2
user data value pairs into facts on a host at instance spin. When I pass
environment = whatever, I want that environment value to override the
agent's puppet.conf environment value. I'm trying to achieve this
currently with another custom module:

require 'facter'
if Facter.value('environment')
envstring = Facter.value('environment')
$environment = envstring
else
envstring = ''
end

Please let me know if this is just way off base including any way this
might be possible.

Thanks In Advance,

Joel