I have had a think about it, and can offer a middle ground approach to clerical transformations combined with psionics. How?
Quite simply, epic clerics possessing epic psionic abilities can cast psionic enchantments, but because divine magic does not blend quite as well with psionics as arcane magic, they can never apply the advanced being subtype using their spells. What this means is that while they can cast psionic enchantments based on the metamophosis seed and undergo changes, they never access advanced being salient feats.
I think this is an excellent compromise, and I think I will roll it into my framework. Below, the psiotheology skill. Its a pared down divine version of the psiotheurgy skill.
Psiotheology [Epic] [Psionic Enchantment]
This feat gives access to the skill Knowledge (psiotheology), which is psionic enchantment as a field of study. Psiotheology enhances the characters ability to use metamorphosis magic and divine epic spells when those spells are bolstered by expending an epic power slot at the same time.
Prerequisite: Epic spellcasting, epic manifesting, Spellcraft 24 ranks. Knowledge (religion OR nature). Psicraft 24 ranks, Knowledge (psionics) 24 ranks.
Benefit: The character can now take ranks in the Knowledge (psiotheology) skill. Each rank of Knowledge (psiotheology) provides +1 psiotheology bonus to Spellcraft checks of epic spells using the if an epic power slot is expended while casting the epic spell.
Gentle Metamorphosis (Ex): You can use the metamorphosis spell on yourself or another creature without the spell counting towards the maximum 10 uses of metamorphosis that a single creature can withstand. When casting gentle metamorphosis, you may not use a focus structure (a singular exception for the Pristine Tower). You can cast one additional metamorphosis on an individual (or yourself) without counting against the ten-time limit once for every 12 ranks you have in this skill.
Psiotheology benefits do not stack with psiotheurgy and vice versa.
New Skill: Knowledge (psiotheology).
This skill grants knowledge of divine magical and psionic manipulation. There are no skill checks for this skill. Each rank in this skill provides +1 psiotheology bonus to Spellcraft checks of epic spells using the if an epic power slot is expended while casting the epic spell.