Create an additional field to hold the value and pad based on the '.' for the max length. then index on this field. So the result would be (if max length is 4):

1 0001
1.1 0001.0001
1.1.R 0001.0001.000R
1.R 0001.000R
1.R.1 0001.000R.0001
2 0001
03 0003
5.R 0005.000R
10 0010
12.R 0012.000R
A 000A
B 000B
AA 00AA