Using IV Bag to autodose ferts?

Yes, people have done that. IIRC there were bags sold specifically for that purpose.
There are a few problems with that... Positioning the bags above the tank, the drip lines clogging over time, salts settling out on the bottom, leading to inconsistent dosing.

From a medical standpoint that sounds awesome, but as per the previous comment they are right with the salts settling at the bottom and clogging of tube lines. When using IV bags in the hospital setting we must flush the lines daily to prevent the clogging and to make sure the medications are running smoothly. So with that said you still need to maintain the lines daily, and if you dose your ferts daily already there's no point in setting up the IV, UNLESS you just put the daily amount you want to dose with in the IV drip so it will release slowly throughout the day.

I was just thinking -- how awesome would something like this be for spot treating algae? You could position the drip line directly over the algae and have a slow drip of something like Excel (obviously not to exceed the tank's daily dose) going slowly and directly into the infested area. I might actually try this on a particularly stubborn spot that is close to a window.

I like High Desert's idea! But I wonder if that slow a dose would get spread around the tank too fast?
Part of why syringing the algae with Excel or Hydrogen Peroxide works is that for several minutes they are exposed to a very high dose of the material. Then you turn the filters back on and that dose is dispersed through the tank.
If the dose is spread out over several hours and the filter is still running then the material is not building up in the area of the algae.

I'd save them for acclimating livestock. They usually come with a roller clamp that you can manually adjust to X drops per second.