Is there a way to specify the amount of an item I want to sell without having to hold the mouse button down?

When I have a lot of plutonium, I like to sell my excess. I typically like to keep about 1,000 on hand, and sell the rest. However, its annoying to have to wait while I hold the mouse button down so that I can sell the proper amount.

For example, if I have 4,000 plutonium, I would sell 3,000 of it. I have to hold the mouse button down until the amount I hit is 3,000. I would like to instead just type in 3,000 and sell it, but I haven't noticed a way to do this. Is this functionality in the game and if it is, how do I do it?

Move what you don't want to sell to your ship (or from your ship), then you can sell it in bulk at the right amount. I always keep one full slot of each element on my ship (except iron or carbon), so I know that anything I hold in my exosuit is OK to sell.

For your example, as each full slot in exosuit is 250 units, I'd move 4 full slots to the ship, then sell anything left.