Complex Passback Scheme

[posted from inbound support]
I’m trying to set up passbacks for use with a panel provider. At their end, respondents will enter the survey, be directed midway to the surveyengine survey component, then be directed back to their survey as a re-entry in their system to complete the last part (and to be identified as completing the survey). I’ve followed the advice in re passbacks but the issue is that they require that their text re reentry is the final part of the passback, rather than the appended ID.

i.e. what we are getting is like this:

xxxxxxxx?__userid=exampleid&__qid=reentry&userID=123456

whereas what they want to receive is like this (ending in their reentry not the ID):

xxxxxxxx?__userid=123456&__qid=reentry

Is there a way to code it so that it appears midway through the passback rather than appended to the end? I tried following some advice online which said to put [userID] in the place where I wanted it, but it didn’t work.

Thanks in advance

Jemimah