Thanks @Nash for looping me in, I can assist. @route_map the closest you can come with the options in Dashboard in mixed mode WPA1+WPA2. Drop me a private message and I'll get you set up via Meraki Support to enable the feature on the back-end. Once enabled, on the Wireless > Access Control page, you'll also see a "WPA1 Only" option in the drop-down options.
Regards,
Dave