There is the possibility to introduce a hack in LittleChef to add ssh key forwarding, but it would be quite ugly. This needs to be solved upstream, in the fabric and paramiko libraries. There are already issues for that:
https://github.com/robey/paramiko/pull/21
fabric/fabric#72

I added a comment there so that they know we would also like to have that feature.

It seems only final testing needs to be done, so we'll keep track of the issues and when paramiko and fabric versions come out we can check it out

Thanks. Out of curiosity what would the hack be. The reason I ask. I have a chef-solo deployment of multiple apps, but it's integrated with vlad the deployer. I really like littlechef. However, I am blocked converting from vlad to littlechef until we can do forwarding.

I don't mind holding off on it, I just would hate to see it delayed for many months. Littlechef would actually solve a few problems I am currently facing in my existing setup.

The hack is explained here: http://lincolnloop.com/blog/2009/sep/22/easy-fabric-deployment-part-1-gitmercurial-and-ssh/

Basically, instead of calling fabric's run command you would call:
local('ssh -A %s "%s"' % (env.host_string, mycommand))

How would you need to patch LittleChef?
The command that needs the ssh forwarding is the one that calls chef-solo (since that is the one which will do the git checkout from the cookbook). That means you would need to change this line:
https://github.com/tobami/littlechef/blob/master/littlechef/chef.py#L292

so that instead of
output = sudo('chef-solo -l {0} -j /etc/chef/node.json'.format(env.loglevel))
it becomes:

cmd = 'sudo chef-solo -l {0} -j /etc/chef/node.json'.format(env.loglevel)
output = local('ssh -A %s "%s"' % (env.host_string, cmd))

Just try it out and tell us how it goes!

This has been fixed upstream in fabric 1.3.5/1.4.0

This means we can implement support in LittleChef by passing -A to Fabric, as documented here