Lisa:
For poor lip seal, I have found it helpful to have mom gently tap around
outside baby's mouth in a circle (above the orbicularis oris muscle) to
increase it's muscle tone immediately before feeding.  For the tongue, I would
recommend sublingual pressure (a fingertip placed GENTLY under the chin, just
behind the mandible, to give input and support to the muscles of the tongue).
Mom can SLIGHTLY increase the pressure or stroke toward the front of the chin
when the baby is doing something wrong with the tongue to redirect tongue
motions. From all the things you said about this baby, he sounds very
hypotonic.  Flexion, body alignment and support are vital in hypotonic kids,
to allow them best function of their oral musculature. It was not surprising
that your other clicking baby nursed better in prone (laying on the mom as she
laid back) this is a common observation in the OT/PT literature.  I would want
to have the 2 mo old baby seen by an occupational therapist who is trained in
SI (sensory integration) or NDT (neurodevelopmental therapy).  Kids with SI
disorders tend to look fine in a gross neuro exam, but have developmental
delays, subtle tone problems, oral motor difficulties (feeding and speech),
and are sometimes very picky about how they are held, fed, bathed or handled.
 Does this baby sweat a lot while nursing?  vomit a lot?
        My 8 year old son has an SI dysfunction, he constantly dropped my
breast, took forever to feed, vomited after every feed, and is still slightly
hypotonic, after 6 years of therapy.  He's also on the honor roll, and reading
8th grade level, so the prognosis is not grim!  Some kids have learning
disabilities, but I happen to think those are the bottlefed ones! :-)
        Catherine Watson Genna, IBCLC