For conditions such as POTS (Postural orthostatic tachycardia syndrome) which are unable to regulate appropriate blood pressure / HR on postural changes, they are treated with volume expansion - like an effective chronic hypovolemia - even though technically they are euvolemic.
Various treatments for these conditions include salt tablets and water intake, or regular home IV saline infusions. These have to be done regularly, however, or healthy kidneys will eliminate the excess fluid.
I recognize that unfortunately, it seems to be hard to get, as wikipedia explains in the article on albumin:
For patients with low blood volume, there is no evidence that albumin reduces mortality when compared with cheaper alternatives such as normal saline, or that albumin reduces mortality in patients with burns and low albumin levels. Therefore, the Cochrane Collaboration recommends that it not be used, except in clinical trials.
However, this research all seems to be about treating acute hypovolemia, such as in cases of blood loss or severe dehydration. In those cases, saline works just as well while being less expensive.
But for EDS patients, the problem isn't low blood volume, but inability to regulate that volume. Saline boosts the quantity of fluid while decreasing oncotic pressure, which is ultimately self-defeating. Maintaining oncotic pressure would, in theory, be ideal. Perhaps we could find a colloid that the kidneys will not eliminate rapidly.
Can blood volume be chronically increased effectively with colloid volume expanders?