I make some GURPS content from time to time, and it takes me a long time to make it. So, since it takes me a long time to do that, I thought I'd start a blog so that my GURPS stuff would exist for all eternity. I plan on posting assets, conversations about complicated rules, session recaps, etc. I dunno if this will be useful to anyone, or only useful to myself, but here we go.
This was actually something of a stumper for me, but I suddenly solved the mystery, so yay. It's a bit more obtuse, and probably more expensive than the better ways to do it, but who cares!
This is actually rooted in the Control (Gravity) advantage from Powers, so let's see how we need to modify it for prayers.
Lower gravity only
Only affects inanimate things we are carrying
Can't cost FP
It must work without concentration
Gravity is considered common, so it is a 20 point/level advantage.
Only affecting inanimate objects, only affecting things we touch, not usable for combat, and only lowering gravity is about 1/16 accessibility, which is worth -40%. Normally, Control only affects things we can touch, unless it's a force, so it does have a bit of an area effect built in, so we can include that in the accessibility. We need the Independent modifier from Powers that is +40% that allows us to not concentrate on it. All together, we have a -10% discount when we include the power modifier.
Learned Prerequisite: Divine Favor 9, IQ + Power Investiture equal to 16 or greater
Learned Prayer Cost: 11 points
With the help of your god, the weight of your burdens are reduced by 30%. Only works in area with normal sanctity or better.
Statistics: Control Gravity 3(Divine, -10%; Accessibility, Inanimate only, Touching only, No combat functionality, lowering gravity only, -40%; Independent, +40%)  + No Nuisance Rolls (Control Gravity 3)
And the improved version:
Seriously Lighten Up!
Learned Prerequisite: Divine Favor 16
Learned Prayer Cost: 38 points
With the help of your god, the weight of your burdens are reduced by 50%. Works even in low sanctity.
Statistics: Control Gravity 5(Divine, -10%; Accessibility, Inanimate only, Touching only, No combat functionality, lowering gravity only, -40%; Independent, +40%; Cosmic, No Roll Required, +100%) 
This is a really expensive approach. Other approaches might be Lifting ST with limited to encumbrance effects only for things you need to actively use, or Payload modified to not count against encumbrance for things you might not use immediately. There are some pros and cons if you dissect each of the three methods. Using Control Gravity, the advantage scales. Using Lifting ST, the ability is cheap, but it doesn't scale as well and calculating the difference between Basic Lift when the power is on or off is a bit of a pain compared to reducing the weight of your burdens by a given amount. Payload is the cheapest, but you can't use things without first extracting them, at which point they do count against encumbrance.