Linking IDs across longitudinal surveys without using contact list triggers

Hello,
I'm working on a longitudinal project of university students where the first phase of data collection has already been collected. The first phase of data collection was set up as 2 surveys with survey 1 collecting identifiable information (email addresses) and generating a unique random ID, and then a second survey with some questionnaires which the unique ID was passed on to as embedded data. This was done so that identifiable information was stored separatelty to sensitive data. We have three further data collection points and I'm trying to find out if there's a better way of linking future data to current data than just repeating this process each time and merging the IDs based on email addresses.
Unfortunately as far as I understand we're not able to follow the advice given by qualtrics (https://www.qualtrics.com/support/survey-platform/common-use-cases-rc/pulling-data-into-a-second-survey-longitudinal-surveys/) to use the contact list triggers or XM directory task as the email links have to be sent out through a university system, and we need the emails to go out at the same time (rather than based on a specified period since they completed the first data collection point).
Any suggestions would be very welcome!
Thank you,
Katie