Objects with xsi:type in Savon 2

Question

I'm trying to create the following soap envelope but I can't add a type and VALUE at same time in some object

<env:Envelope>
    <env:Body>
        <typens:SendRequest>
            <typens:someStuff>123</typens:someStuff>
            <typens:someAuthStuff xsi:type="somenamespace:SomeObject">VALUE</typens:someAuthStuff>
        </typens:SendRequest>
    </env:Body>
</env:Envelope>

This is my message:

client.call(:send, message: {
  someStuff: 123,
  someAuthStuff: { '@xsi:type' => 'somenamespace:SomeObject' },
 }
)

But...How can I add the 'VALUE' in someAuthStuff?

Very similar question as How to use objects with xsi:types in Savon but now in Savon 2.x