Can IAM role temporary credentials be used in cloudformation templates?

I'm building a stack that needs access to a private S3 bucket to download the most current version of my application. I'm using IAM roles, a relatively new AWS feature that allows EC2 instances to be assigned specific roles, which are then coupled with IAM policies. Unfortunately, these roles come with temporary API credentials generated at instantiation. It's not crippling, but it's forced me to do things like this cloud-init script (simplified to just the relevant bit):

#!/bin/sh

# Grab our credentials from the meta-data and parse the response
CREDENTIALS=$(curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/s3access)
S3_ACCESS_KEY=$(echo $CREDENTIALS | ruby -e "require 'rubygems'; require 'json'; puts JSON[STDIN.read]['AccessKeyId'];")
S3_SECRET_KEY=$(echo $CREDENTIALS | ruby -e "require 'rubygems'; require 'json'; puts JSON[STDIN.read]['SecretAccessKey'];")
S3_TOKEN=$(echo $CREDENTIALS | ruby -e "require 'rubygems'; require 'json'; puts JSON[STDIN.read]['Token'];")

# Create an executable script to pull the file
cat << EOF > /tmp/pullS3.rb
require 'rubygems'
require 'aws-sdk'
AWS.config(
    :access_key_id     => "$S3_ACCESS_KEY",
    :secret_access_key => "$S3_SECRET_KEY",
    :session_token     => "$S3_TOKEN")
s3 = AWS::S3.new()
myfile = s3.buckets['mybucket'].objects["path/to/my/file"]
File.open("/path/to/save/myfile", "w") do |f|
    f.write(myfile.read)
end
EOF

# Downloading the file
ruby /tmp/pullS3.rb

First and foremost: This works, and works pretty well. All the same, I'd love to use CloudFormation's existing support for source access. Specifically, cfn-init supports the use