How to use WSUS API

If you do not have them on a domain, you could import the relevant settings via a registry file. So to directly answer your question, no you can't. Even in a domain environment you are still configuring them by group policy. Everything takes configuration, I think you are just looking for the simplest way. Running one batch/reg file per machine is going to take less time then setting them up manually.

Reference: Configure Automatic Updates in a Non–Active Directory Environment

Sample:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\WindowsUpdate]
"ElevateNonAdmins"=dword:00000001
"WUServer"="http://WSUSServer.OrIPAddress:8530"
"WUStatusServer"="http://WSUSServer.OrIPAddress:8530"
"TargetGroupEnabled"=dword:00000001
"TargetGroup"="Workstations"

[HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\WindowsUpdate\AU]
; 'Install Updates and Shut Down' option will be available in the Shut Down Windows dialog box if updates are available
"NoAUShutdownOption"=dword:00000000
"NoAUAsDefaultShutdownOption"=dword:00000000
; False (Do not disable AutoUpdate)
"NoAutoUpdate"=dword:00000000
; 4 – Scheduled install (valid only if legal values are also specified for ScheduledInstallDay and ScheduledInstallTime).
"AUOptions"=dword:00000004
; Every day at 8 AM
"ScheduledInstallDay"=dword:00000000
"ScheduledInstallTime"=dword:00000008
"RescheduleWaitTimeEnabled"=dword:00000001
"RescheduleWaitTime"=dword:00000001
"AutoInstallMinorUpdates"=dword:00000001
"RebootRelaunchTimeoutEnabled"=dword:00000001
"RebootRelaunchTimeout"=dword:0000000a
; Allow reboots with logged on users
"NoAutoRebootWithLoggedOnUsers"=dword:00000000
"UseWUServer"=dword:00000001

I don't believe so, but one workaround is to implement an intercepting proxy server on your network. This means that you can configure the WSUS server to instruct clients to download from Microsoft, but still cache the content locally for machines on your network. (As an added bonus, updates will only be downloaded if they are actually needed, so you can be less selective about what you approve.)

A variation of this is to configure WinHTTP on your desktop machines to use a proxy server, although this means laptops that are on-site will still download from Microsoft. In principle you could write some software that detects the current location of the machine and reconfigures WinHTTP as necessary.