Since no one would have to be around to monitor the boil, you could set a timer to bring the water up to the boil at night when the kettle goes unused anyway (assuming you aren't running three shifts). The next day you'd have room temperature water ready to go. As far as blending, no reason you'd have to do it inline. Just keep an eye on your sight glass/volume markings/whatever during transfer or filtration, stop at the correct point, and top off with water. Maybe recirculate for a few minutes to get it mixed, if that turns out to be necessary. As someone else pointed out, you could also do it in two batches and avoid the need for a double-size bright tank.
I was more referring back to the original poster's scenario of not wanting to purchase larger equipment and instead blending. My assumption was since the scenario opted not to use larger tanks, he wouldn't have the capacity to hold all of the liquid to blend in-tank.
I also approached it financially, which adds some voodoo to the mix.
You have to ask yourself if the capital costs of larger tanks is greater than the additional cost of energy over time. And to do this you need to see where those costs occur and how they are managed in a financial statement.
The tanks are initial capital costs which are depreciated over time. It's usually a fixed value and very predictable. The additional water and energy and labor required to create the dilution are part of the cost of good sold. These are not fixed costs but are variable. The cost of consumables and energy fluctuates with market prices. So if one year it costs you $1.00 to brew a batch of beer, the next year it may cost you $1.05 to brew the same batch of beer. With more variable costs the ability to predict and project profitability over time becomes less probable. Additionally, the more batches you make the higher the labor cost because of the additional step of blending. Even if it only increases labor by .5x, it's still a .5 increase with each batch.
Where does this burn you? In your growth phase, which usually begins around years 3-4. Inefficient business processes cost money and become expensive as you grow. It's very difficult to improve efficiency during a growth phase, so capacity planning is key. It's also very difficult to do.
It's understandable that if you don't have enough capital at the onset you may need to look at different kinds of business process to compensate. However, part of your business plan should include a path to improve or correct those processes as an ongoing exercise instead of realizing during a growth phase that you need even more capital to correct them.