There is a workaround, but it requires 3rd party software:
Download a utility capable of executing a scroll wheel simulation macro, triggered by a keyboard shortcut.
I'm using Keyboard Maestro which is an incredibly powerful tool in its own right.
I've created four global macros, each one simulating Scroll Wheel Up/Down/Left/Right.
The scrolling value can be set as low as 1 pixel ⚠ per keystroke. (I'm fine with 5…)
Each macro gets a global keyboard shortcut:
⌃⇧⌘↑
⌃⇧⌘↓
⌃⇧⌘←
⌃⇧⌘→
(These modifiers are optional, but over the years I've developed the habit to use ⌃⇧⌘ strictly for global shortcuts active in all applications. This habit avoids possible conflicts with internal application shortcuts, because this modifier combination is rather uncommon.)
To get contiunous scrolling while holding the keys down, make sure the hot key trigger setting is "is down", not the default "is pressed".
Also note that the pointer must be over the affected window – same as if you'd be using a real scroll wheel – for the shortcuts to work.
It works in all application windows which support scroll wheel input, including text forms like this one I'm posting this reply.
Hope that helps