This is the idea I came up with to use the Heal skill. It's intended to complement the ability of party healers, and give them incentive to keep putting skill points in the Heal skill, since it will increase the effectiveness of their healing spells. The wording is not the greatest, but it will do for now, I hope
Heal Skill:
Magic is notoriously fickle and unpredictable. Nowhere is this more obvious than when a cleric is calling the power of his deity to heal a comrade. Even the most powerful cleric can be frustrated when his powerful healing spell has decidely less than full effect. However, clerics (or other casters who can cast cure spells) who are knowledgeable in the anatomy of their patients and adept at even the mundane caring of the sick and wounded can use this knowledge to focus their healing magic; when given enough time to study their patient.
Check:
On a succesful check, the caster can add a bonus to his d8 rolls for a cure spell on a single recipient of the spell. The resulting dice roll cannot be greater than the highest possible roll.
DC 25, add +2 to each d8 to a maximum roll of 8
DC 35, add +4 to each d8 to a maximum roll of 8
Example: 3rd level cleric, with 6 ranks in Heal, a Healer's kit and the self sufficient feat (total bonus, +10) has a patient with a sword wound to abdomen and spends a minute assessing her wound. At the end of the minute, he makes a Heal check, and rolls a 16, thus making the DC 25. He then casts "Cure Light Wounds" and rolls a d8. Basically, he takes whatever he rolled on this die and adds 2 to the roll, to a maximum of 8, adds his level to the spell as normal (3) and there's the damaged healed.
So if he rolled a "4", he would treat it like a "6". If he rolled a 6, 7, or 8, he would treat it like a "8".
If he cast "Cure moderate wounds" instead, he would roll two "d8's", adding 2 to each roll, to a maximum of 8 for each die. So if he rolled a 4 and an 8, he would treat it as a total roll of 14 (+3 for his level, so he would heal a total of 17 points of damage).
Action: The caster must do nothing but study the recipient of the cure spell he will cast for 1 full minute. If he is interupted in any way, he must restart his studying for another 1 minute. At the end of the minute, the cleric casts his spell and applies any benefit to the dice roll. The cleric may not take 10 on the skill roll.
Try Again: The caster can only attempt this skill once for any given cure spell. He may try again, but uses up a cure spell (which must be chosen before the skill attempt is made) for each attempt of the cure spell.