Interesting issue. If you could add a little more clarification as to the file being parsed that would be helpful.
i also dont recall a 2220 loop in this schema, so, i am going to assume that you are referring to the 2200D and E loops (subscriber and dependent) which are controlled by the parent 2100D and E, that are controlled by the NM1 01 qualifier. Anyway, with that jabble out of the way, you can change the REF and DTP segments (which repeat) to choice rather than sequence, but if they decide to send a REF then a DTP then a REF etc, thats a little more complex. Youll need to have the two nodes as choice but repeating, which wouldnt really work if its haphazard.
But, with my experience in Healthcare and with the 277, the client probably wont do that, they probably miscoded the file to be exactly the same everytime (except for whether or not they will have a dependent), so i would suggest customizing a schema for them and make it more rigid (ie, always returns in their sequence) and use the standard schema for everyone else. then you would map the resulting message to the standard 277 schema and feed it through your current process.
Hope that helps. if not, please include a snippet of EDI (dont forget to remove and PHI)