We configured MultiSite for each different location of our offices. DA setup only allows the option between preconfigured location or automatically and allowing the user to change the location.
However, the latter does not provide any method for selecting what the default site should be for clients. This can result in clients connecting to a site closer (read: lower ping) but actually not preferred route due to bandwidth restrictions.
This is done by setting SYSTEM\CurrentControlSet\services\iphlpsvc\DaMultisite\UserSelectedSite to one of the DirectAccess site's GUID. Also SYSTEM\CurrentControlSet\services\iphlpsvc\DaMultisite\SelectionMethod needs to be set to 2.
Effective after a reboot of the client or restarting the IP Helper service.