How to specify read structure with variable UMI length?

[bounlu]

Referring to this comment, if I have variable length of UMIs 5, 6, 7 and 8 bp long plus 2bp arbitrary seq, how should I specify them in the read structures and how to utilise --min-umi-length? Basically I want to handle the below cases at once:

5M2S+T 5M2S+T
6M2S+T 6M2S+T
7M2S+T 7M2S+T
8M2S+T 8M2S+T