Thank you for you answer. A scaling option would be a nice addition. I've been looking at the RM cleric list called "Life Mastery" and I can find two spells that sounded appropriate but neither does the job:
Heal Life Essence I — The target of this spell is any being who
has suffered some amount of soul damage. The target will be
healed of d10 points of lost temporary Constitution. See
RMFRP Section 24.0 (p. 75) for more information on soul
damage.
Restoration — The target of this spell is any being that has
had his mental capabilities hindered (e.g., from the Mind
Erosion spell list). The target of this spell will recover lost
experience. However, recovery is not always complete. The
amount of experience that is not recovered is 1% for each day
that the target suffered from the condition. For example, if a
target lost 10,000 experience points and it took him 20 days
to find a Cleric with this spell, he would only recover 8,000 of
the lost experience points.
Heal life essence True (further down the list) bolsters the amount of con points healed.