Hi,
So based on the thread that you provided i was able to make it work 
The example that i am using right now is:
var deliveryId = nms.delivery.SubmitDelivery(templateId,
<delivery>
<targets>
<deliveryTarget nonEmpty="true">
<targetPart exclusion='false' ignoreDeleteStatus='false'>
<where>
<condition expr={"@id='" + recipientId + "'"} />
</where>
</targetPart>
</deliveryTarget>
</targets>
<content addExtraObject="true">
<html>
<source>{abc}</source>
</html>
<extraObject array="true" jsName="testing" schema="cus:schema" startPath="/">
<custom>
<select>
<node analyze="false" expr="@field" label="" />
</select>
</custom>
<where displayFilter="primary key of recipient" filteringSchema="cus:schema">
<condition expr={"[Recipient/@id] ="+recipientId}/>
</where>
</extraObject>
</content>
</delivery>
);
So, i had to change the method to Submit Delivery and add the "extra Object" to the XML.
Thank you for your help!