Rationalizing it is easy if you use the QP/XP equivalency that my campaign did when we went to divine PCs. We used the notion that 1 QP was worth 25 XP to allow for deities to expend personal power (their QP) to raise mortals connected to them to higher power levels, directly.
It was, after all, true that in 1E and earlier editions, hit points and other benefits of higher level were said to not only be the result of greater learning on the part of the high-level character, but also the result of the favor of higher beings like gods (who naturally have the power to grant favors like miraculous escapes from certain death, for example a Reflex save against a Fireball allowing the Rogue to take no damage at all despite being squarely within the area of effect of the explosion- while a Commoner who was in the explosion with the Rogue would certainly be roasted to a crisp).
The fact that the conversion of XP to QP and vice versa involved some loss (not precisely the 1-for-10 rule in the IH, but similar) meant that we didn't allow direct one-to-one transfers- but if, for example, you got enough XP to raise your HD to a number higher than that allowed by your present divine tier and template, then you are allowed to convert extra XP to QP directly- using a formula of 50 XP = 1 QP (if memory serves. I may be wrong, it's been years since I used these formulas). OTOH, if you have enough QP to go up to the next divine tier, but you don't yet meet the HD requirements, then you can spend extra QP to get XP and raise your HD more quickly. I think we went with 1 QP = 5 XP in that case.
But this meant that since mortal priests are supposed to get power from the deity, and likewise beings such as your Prophets, then you should likewise be able to spend QP to help mortals by giving them HD (and hence, level-ups) as well. So we worked out a system for that too. The rule we used, in the end, was that if the mortal has a direct connection to you the deity spending the QP- by which I mean, the mortal is your priest, or has a 1-or-2-DR Divine template from you, or is your actual child somehow, then you get to spend the cheapest amount: 1 QP from you gives the mortal 1 XP. If the mortal is none of the above, but is still connected to you in some manner, such as being a follower of your religion, or being a grandchild or similar second-order relative, then you can spend 2 QP to give the mortal 1 XP. Mortals outside even that category are the most expensive; they need to have 4 QP spent to give them 1 XP.
These numbers look expensive at first glance, and they certainly are for deities at the level of Demigod or so- but consider for a moment what sort of power Greater Deities can throw around. A Greater God has hundreds of thousands of QP to spend on "petty cash" without really making a dent in his QP total- and a mortal only requires 1000 XP to go from 1st level to 2nd.
So yes, when my PCs reached the higher divine tiers, they started using this option and other similar ones (such as making new races of beings) to do some significant minion-creating in the game world. One PC not only declared an assassin who'd been a favorite companion of hers as her Prophet, but also proceeded to give him over 70 levels, bringing his total to 100 (recall that, in my game, I had vastly different numbers of HD required for each divine tier- Greater Deities for example have a 400 HD minimum). IMO, this option for minion-creation really enhanced the game, in a lot of ways. The players certainly seemed to like it!
