associate text with chords

[achar]

Hello. Here is a piece of code to explain my problem. I would like the 
roman numerals of the mib7 chord as well as that of do7 to be located 
under the chord names. But the text is associated with a note or a rest 
so I can't do it. Does anyone have a solution? Thank you. P.S.: I 
already received answers but, they evaporated before I could read them

<<
  \chords { bes2:m7 ees:7
  s1
  g2:m7 c:7
  }
  \new Staff \relative c''
  {
     f4_"ii / V" aes2 g4_"V7 /IV"
     R1
     \break
      bes1_"iii m7 - V7 / ii" |

      R1
     \break

  }
>>