In such cases, I mostly resort to enumeration:

   /(0[1-9]
   |1[2-9]
   |2[3-9]
   |3[4-9]
   |4[5-9]
   |5[6-9]
   |6[7-9]
   |7[8-9]
   |8[9-9])/
[download]

will only capture pairs where the first digit is lower than the second digit. I'm not sure that there is a smarter/nicer version of that though ...