Auto-size: Grow text frame width with max-width set?

Hello,

My setup:

I am using a text frame auto-size for a photo caption.

The photos and captions are created via a data merge.

The caption is anchored to the bottom of the page so it grows vertically upwards depending on length of caption text.

Some captions are a few words long, while other captions are multiple lines long.

The caption text frame, currently, is set to a defined width; when the caption text meets that width, it wraps, and the text frame grows upwards.

My desired goal:

I would like to have a text frame that grows, width-wise, with the first line of the caption; if/when the caption text is long enough to wrap, I would like the text box to stop growing and allow for the text to wrap. Essentially, I would like all of the features I have specified from above, but I would like the text frame to shrink-wrap the text until it meets a specified maximum width, and then have it grow vertically from bottom (with text wrap, depending on text length).

My questions:

From what I can tell, I don't think what I want is possible without some sort of manual intervention. I would like to avoid doing manual work as there are many pages.

With that said, am I overlooking a feature?

If this functionality is not "built in", can anyone recommend a plugin or script that could help me accomplish this goal?

Thanks so much for reading my question.