Custom Numeric Format: Show Integer Quotient and Remainder

I have a number of months in a cell that I would like to display in years and months (for example, 30.50213 should display as "30 yr 06 mo"). Essentially, I am attempting to show the value of:

=FLOOR(CONTENTS / 12)&" yr "&MOD(FLOOR(CONTENTS), 12)&" mo"

I have tried the following format, which gets me close (change the cell contents into fractional years instead of fractional months):

dd \y\r hh \m\o

The above gets 2*months since there are 24 hours in a day. I have tried the following to try and get the months (hours) to appear in halves to no avail:

dd \y\r hh ?/2 \m\o

Any ideas how I can display my number divided by twelve as well as mod 12 in the same cell using custom numeric formats? Thanks,

-Jeff