The only way around that which I can see is to force the user to enter something like what's below. Alternatively, one could setup a button to show on the basic editor so that they can just click a "spoiler" button to input [spoiler NOW] for them However, with the way the forums work, that means they don't really see a button marked Spoiler, they see a button marked spoiler NOW which looks too odd and would make people wonder what it does. So many little problems using this forum.
Where NOW would automatically get the date or time inserted so that it would be distinctly different than anybody elses. However this would likely need some extra coding that I just don't have the knowledge to do.