The first thing I would look for is a style guide relevant to your awkward position that needs these to be written out. If something or someone is asking you to do this, go to them for the correct behavior.
Aside from that (or convincing them this is a bad idea), I would use a word to split the denominator and numerator (depending on context):
one hundred twenty-four over one hundred forty-five
one hundred twenty-four divided by one hundred forty-five
The other complication in this is how to write compound fractions such as
1 3/4. I use and to split them:
one and three-fourths
six hundred and one hundred twenty-four over one hundred forty-five
This is still annoying and slightly ambiguous, but that is what you get when writing out numbers like these.