Playing subtitles - and only subtitles - on Android
After more searching, I found SubtitlePlayer in the Google Play Store.

It seems to work adequately for what I need, but because its name is two words jammed together, doesn't show up when you search for "Subtitle" in the market.

Also, the page says it needs 'Unicode' subtitles; after a few tries, I got it to work correctly with UTF-8 encoding, without a BOM.