using tf data from bag files

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The main problem is that playing a bag files in conjunction with tf is problematic. Tf messages arent't synchronized with the current rosTime. Several alternatives has been proposed but apparently they don't work (at least not for me in python). See http://answers.ros.org/question/1114/waitfortransform-use_sim_time-python and see also http://ros-users.122217.n3.nabble.com/tf-use-sim-time-clock-and-bag-files-td1305066.html

AFAIK this problem is still not solved for tf in python. I think it would be possible if the TransformListener::subscription_callback were public. Am I right? tf::tfMessage's could be retrieved from bag and pushed manually using this method and the Bag API (see below a pythonic code - pytf.cpp modifications also needed):

bag = rosbag.Bag(bag_file)
listener = tf.TransformListener()
for topic, msg, t in bag.read_messages(topics=['/tf']):
     listener.subscription_callback(msg)

To reproduce bags with tf messages are very interesting specially in geometric learning problems where bags files with transform information can be used as training database (this is my case).

Until now I'm using this solution to simulate tf in a bag messages at the current time(though I don't like it so much):

import roslib
roslib.load_manifest('tf')
import rospy
import tf

rospy.init_node("tf_restamper")
tfpublisher= rospy.Publisher("tf",tf.msg.tfMessage)

def tfcallback(tfmessage):
    for transf in tfmessage.transforms:
        transf.header.stamp=rospy.Time.now()
    tfpublisher.publish(tfmessage)

tfproxy = rospy.Subscriber("tf_old",tf.msg.tfMessage,tfcallback)
rospy.spin()