Hopefully adjusted for the next release.
While I can't make a button-holding action, using right-click (or the context menu action) should now allow spending the maximum available points for that stat (similar operation in the trade/drop screen). Though keep in mind, if that stat is being affected by a pending perk (namely "Steel Will"), then the +"Max" value may act iffy when there's already some points pending on one end (since there's layered calculation being done when the action is called). Starting from (0) is ideal for those instances. Never mind, I fixed it.
If you are not able to right-click, there should be a "Toggle Max" button that appears if there are stat points available to spend/remove. When enabled, it'll spend/remove the max points. When not enabled, it'll function as normal.