Trouble syncing person who is both student and TA from SIS to Canvas

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In our SIS (CAMS), student records and faculty records are entirely separate and if an individual exists in both areas they get separate ID numbers in the SIS for each role and the system has no idea that the two are actually the same individual.  For example, pretend that John Smith is a student with a Student ID of 111111.  He gets synced to Canvas as a student under the SIS ID of 111111.  He then gets asked to be a TA for a different course in the same term.  In our SIS we must create a new faculty/TA record for him (since students cannot be attached to courses as instructors) and that record has a Faculty ID of 222222.  Both records are tied to the same email of jsmith@school.edu but the SIS has no idea that they are the same person.  When the next sync happens between our SIS and Canvas, this person can either have their Canvas user record show his Student ID of 111111 as his SIS ID or his Faculty/TA ID of 222222 as his SIS ID.  Both actually show up in our user csv file and whichever one happens to be later in the file overwrites the SIS ID in the canvas user table.  If his Student ID ends up as the SIS ID in his Canvas user record, then he can see the courses that he is in as a student but not the course he’s attached to as a TA (since the enrollment for that course is under his Faculty/TA ID number); if his Faculty/TA ID shows up as the SIS ID in his Canvas user record, then he can see the course that he is in as a TA but not the courses he’s attached to as a student (since the enrollment for those courses is under his Student ID number). 

Here’s one more data point: if I go into the Canvas user record for John Smith under Admin > People and manually change his SIS ID from 111111 (the Student ID) to 222222 (the Faculty/TA ID) he will disappear from the rosters for the courses he is in as a student and suddenly appear as a TA on the roster for the course that he is TA’ing.  So all of the enrollment records exist behind the scenes, but only the ones that match the SIS ID in his user record show up in the course rosters.  Canvas appears to be functioning as designed, but the limitations of the data in our SIS are causing problems.

The obvious solution is to submit all of his info to Canvas with only one of the SIS ID numbers.  Unfortunately, it is impossible to set up our SIS in such a way because student records can’t be attached to courses as faculty/TAs and faculty/TA records can’t be attached to courses as registered students.  Have any other CAMS schools encountering this problem?  Do you have any suggested workarounds to keep things fully automated?  Our current solution is manually changing the TA data after it is imported into Canvas, but this is not realistic for the long term given our size.