If you are only testing intercepts or thresholds, MIMIC and multiple group are the same. So I wouldn't make a big deal of which approach you are using. The advantage of multiple group over MIMIC is that you can test the equality of factor loadings and other measurement parameters. If these parameters are not part of the model, it is not an issue.
A small example for one threshold is: MODEL: %OVERALL% %c#1% [u1$1] (1); %c#2% [u1$1] (1);