I almost have something working that uses the concept in this post.
So, you have a hidden (and transparent) button or shape on the page, and you have a conditional on the button/shape that makes it visible when the text input is focused. Then, you use the Do when condition is true workflow to insert a character at the cursor position (via the plugin) when the button/shape is visible. With that setup in place, the character will be inserted at the cursor position when the user clicks in the input field.
There are definitely loose ends with the suggestion above, not the least of which is I didn’t go all the way down the path of trying to split by the inserted character (and the fact that the character is inserted as the first character when the user first clicks in the field). But, the suggestion does get some of the way down the path, and I hope it helps so you can take it the rest of the way.