Hello Ronald,
While it is true you need to swtich do a domain admin context to call the account-list-search function, you do not need the domain administrator password to do the switch.
When you're authenticated as a system admin you can call sysadmin/manage-domain to retrieve an auth token valid for the corresponding domain administrator context and then use it to do your calls on domains admin functions.
Then you can switch back to the system admin token when done.
Well, that's how we did it when we rewrote the SmarterMail implementation in our home made control panel to use the new API instead of the legacy (but easier to use...) Soap API.
Kind regards.
Sébastien Riccio
System & Network Admin
https://swisscenter.com