Like the ones in my sig?
Make a table with one row and x columns (x is how many mini-spoilers you want), and put a spoiler in each slot of the table.
Here's for my three mini-spoilers:
HTML:
[table="width: 500, align: center"]
[tr]
[td][spoiler= ]contents of spoiler #1~[/spoiler][/td]
[td][spoiler= ]contents of spoiler #2~[/spoiler][/td]
[td][spoiler= ]contents of spoiler #3~[/spoiler][/td]
[/tr]
[/table]
Add another "[~td][~spoiler= ]contents of spoiler #3~[~/spoiler][~/td]" (remove the ~'s of course) and edit it if you want an additional mini-spoiler. Edit the width number in "table="width: 500, align: center" to change how wide they are (sometimes makes screwy results), and edit the align to make all the spoilers align to the left, center, or right respectively. Hope this helps!