Deleting user via API leaves SIS info behind

[Ben]

I'm creating a user via the API and setting the pseudonym['sis_user_id']  field.  I can successfully delete this user, but if I try to recreate it using the same sis_user_id i get the following error: 

{"errors":{"user":{"pseudonyms":[{"attribute":"pseudonyms","type":"invalid","message":"invalid"}]},"pseudonym":{"sis_user_id":[{"attribute":"sis_user_id","type":"SIS ID \"54348\" is already in use","message":"SIS ID \"54348\" is already in use"}]},"observee":{}}}

Is there a way to delete the SIS record associated with a student?

Alternatively storing a the user_id in a custom field would work for me, but I'm wary of using the non finalized API for that.

Thanks,
Ben

[Ben]

It seems that the pseudonym[uniqu_id] is also a sticking point:

{"errors":{"user":{"pseudonyms":[{"attribute":"pseudonyms","type":"invalid","message":"invalid"}]},"pseudonym":{"unique_id":[{"attribute":"unique_id","type":"taken","message":"taken"}]},"observee":{}}}

I wonder if I'd be better of not deleting users and just taking them out of courses instead...