Thanks to our colleagues who are working on the updated TG Guidelines! They say that although transcription of mixed numbers below a number line is not explicitly covered in those guidelines, UEB Math/Science transcription of time labels (e.g., 1:30) is and a3#cj is the recommended transcription for the time 1:30 below a number line. So, it makes perfect sense that b#b/e would be the appropriate transcription for "two and two-fifths."
–Kyle