Thread:User talk:CodeCat/biplaza and other Spanish adjectives

Hi CodeCat. I see you recently made big changes to Template:es-adj. Thanks for that, you always do great work with templates, although it means I usually have to relearn them every few years...Anyway, I just made the page biplaza, which has two plural forms - it is usually invariable, so has plural biplaza, but it can also have a "regular" plural form - biplazas. How could I show this using Template:es-adj?