[EWS][E2013][SOAP] Can I set first-day of week?

I can retrieve the first day of the week using OWA User options with SOAP:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:typ="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:mes="http://schemas.microsoft.com/exchange/services/2006/messages"><soapenv:Header><typ:RequestServerVersion Version="Exchange2013"/></soapenv:Header><soapenv:Body><mes:GetUserConfiguration><mes:UserConfigurationName Name="OWA.UserOptions"><typ:DistinguishedFolderId Id="root"/></mes:UserConfigurationName><mes:UserConfigurationProperties>All</mes:UserConfigurationProperties></mes:GetUserConfiguration></soapenv:Body></soapenv:Envelope>

(How) is it possible to *set* FirstDOW?

I need to force that from program code for a syncing app, in case users have different FirstDOW settings.