Hi Rachel, most of our programs for top talent include pre and post activities. Drip learning is critical in pulling through the concepts and truly changing behavior, building relationships etc. A few ideas from easy to hard that don't rely on specific technology (if you have tech even easier):
Assign them into small teams for the in-person event and have them work with those teams on some of the table activities to build relationships. Then encourage them to peer coach each other and remind them to do so each month. If you can have them set up their first post-event conversation on the last day of the in-person event you'll have the most luck. Set up a place to post pictures, ah-ha's, etc.
Share a resource tied to the program objectives and nudge the cohort to discuss it/ share thoughts on MS Teams, Slack or whatever you use (2 min video, brief article, etc.). Red Thread research shared top learning methods by management level, I can't find it online but Sr Leader was internet, prof network and articles.
Have an online session featuring an internal or external leader. Allow time for the topic and 20 min for breakouts to discuss in small groups.
Capstone or incubator...let them pick their project or give them something that has already been identified as a need by top leadership.
Just a sampling, there are so many ways and worth doing tailored to program goals. If they come in for the 3 day event, leave, and never do anything else than it may be more about retention than learning (also important, just different).