However, you could potentially use "plop" or "plunk" as a prefix in a creative context, like:
* Plopper: A person who plops down on a seat.
* Plunkster: A person who plunks down their money.
These are not official words, but they demonstrate the potential to use "plop" or "plunk" in a prefix-like way for playful or informal contexts.
Is there a specific context you're thinking of?