It would be great to have the option of manually setting the amount of gold you want to donate to your alliance.
Let’s say you have a level 8 Alliance Tower, you can donate 100,000 gold every day.
For reasons that you just want a fraction of that amount to donate, you can input the amount manually.
If you think this might be too much of an advantage in securing your gold down to your protected limit,
then I suggest that once you donate regardless of amount, the cooldown for donating starts immediately.
It is still advantageous for you, but not for your alliance in the long run.