G'day raygun,

As ++ikegami has explained, and you have accepted, there is no compatibility composition.

You have asked about modules. There are some available but I can't say whether they are suitable for your purposes (as you haven't explained that part). Here's a couple. If these aren't suitable, search MetaCPAN using terms reflecting your use case.

• HTML::Fraction may do what you want if you're working with HTML.
• Unicode::Fraction will render any vulgar fraction into something that's intended to look like a Unicode fraction: 12345/67890 becomes something like ¹²³⁴⁵/₆₇₈₉₀ (that's just a rough approximation).

"... write my own function to handle these fractions (there are only a dozen or so), ..."

There's actually 18 in total. Three have the codepoints U+00BC - U+00BE and can be found in the PDF Code Chart "C1 Controls and Latin-1 Supplement". The other 15 have the codepoints U+2150 - U+215E and can be found in the PDF Code Chart "Number Forms".

Writing your own function is pretty easy. I wrote one just for the fun of it: I've put it in a spoiler so as not to spoil your fun if you wanted to do this, but do feel free to look and take any code or ideas you want.