This is a really hard question since I don't think you can really say anything would work until you try it. I like the pressure cooker idea.  I think what you say is good, but I do not know if it the pressure cooker would actually seal. My pressure cooker has a rubber ring that looks like it would only work in one way (pressure on the inside, pushing out.. not the other way) But it is easy enough to try without ruining the pressure cooker -- just connect a vacuum tube to the release valve.

I know aspirators can boil water at room temperature, if the water is colder than room temp. If you were to put it on a magnetic stirrer hotplate, and had the stirrer and heater on, you could probably get it to boil pretty furiously with the agitation and added energy.

The only other possible thing I can think of at the moment, that would perhaps be possible (I bet much less practical and more expensive) would be to do some sort of reverse osmosis?  http://en.wikipedia.org/wiki/Reverse_osmosis#Process

If you had a membrane, and your molecule in the solution could not pass through it, but the water could, you might possibly be able to have something like a very very saturated + non-dissolved solids of Calcium chloride solution in one side suck away some/most of the water leaving a more concentrated solution of your product.

This, say could reduce your amount of water by maybe.. half a gallon? or more? (again I don't think this is practical, just brain storming)

The calcium chloride solution that has more water in it could then be boiled off at a much higher temperature, and  reused... the other remaining solution could possibly would than have to be vacuum dried again, but you'd have less liquid to contend with.

I'd go with your first idea -- and see how that works out.

Perhaps you can just alter your process and make it so you have less than a gallon of solution to evaporate? Probably not...

You could also get a water pump + aspirator and recycle the water that is being pumped - but that would only be convenient if you already had such a setup.

Might buy some peltier units for the condenser, maybe even a huge heatsink for the pump.

My husband uses an assortment of fry daddies - they range in size from fry grand daddy which will hold a 3 L flask down to the fry baby which he cut the top off of for small scale stuff.  He redid the wiring so he can connect it to a power controller.  I borrowed the small one the other day and I was able to use it with the power controller he created out of a dimmer switch.

Grapeseed is a very good oil to use - it's smoke point is 216.

He's also used electric woks this way but the fry daddy is better because he can immerse almost the entire flask in the oil to get even heating.

Salat

Whenever I need to get rid of large amounts of water (and my desired product doesn't degrade quickly or sublimate quickly) I just buy a dozen or so aluminium turkey trays and set them outside. I'm always surprised at how quickly water evaporates on it's own.

Low heat, a commercial dehumidifier, a "hood" to stop the dehumidifier taking other water from anywhere else in the environment and a little patience should sort this.

Roto vap would still be a worthy construct for many reasons

More info would guide the swarm

Microwaves are great for this. I've used them in the past to evaporate large quantities of cactus syrup. You don't have to worry about scorching plant fats and the evaporation happens quite quickly, from about 500ml to 150ml in just under 20 minutes.

Azeotropic distillation with ether for example proceeds at temperatures you look at and can be arranged easiy as continous distillation to remove the water. Other organic solvents will do it too DCM, chloroform to name two inflammale ones. For the recirculation the needed amount is pretty small.