Sharing or replicating a disk between two VMs in Azure.

Cuurrently finishing up and testing a new "high availability" environment in Azure for a client but running in to an issue. The setup is 2x "app" VMs with their main line of business application (web-based) and IIS, behind an application gateway, all three of which use the same public IP. App gateway simply routes https traffic to app1 unless it does down, in which case https traffc is routed to app2. There is an azure fileshare that is mounted as Z: on both app vms, this is where the application vendor installs their software. The problem is the app vendor's powershell script to install/deploy the software keeps failing due to access denied. The script is ran as local-admin which does have read/write to Z:, but the first step of the script has them naming and setting passwords for three service accounts...and later in the script, I think it tries to use one of those accounts during the install process and fails (access is denied) because the accounts don't have read/write access to Z: is my guess. We azuread joined the Azure fileshare to allow us to adjust its ntfs permissions as a mapped drive, unfortunately this only allows us to grant permissions to AzureAD users/groups, not local accounts such as the three service accounts created by the app vendor. The application vendor has no interest in coming up with a solution on their end for this. so we're stuck and trying to find a replacement for the Azure fileshare, such as sharing or mirroring a data disk between the two app vms. We really don't want to bring in a third-party solution such as a backup or sync tool to do this. Any ideas?