The plugin follows standard Woo rules for this; basically your order will go directly to “Completed” if your order does not “need processing”. The standard rules for this apply when no product in the order “needs shipping” (is “virtual”) and “is downloadable”, but you can modify these rules if you need to.
The simplest way to the goal is to mark your products as “virtual” and “downloadable” on the product editor. The product doesn’t actually have to be downloadable to do this, but it will mark the product as not “needing processing”.
If you can’t do this, then you will need to implement the filter ”woocommerce_order_item_needs_processing’ so it returns true for your products. As mentioned, they will also have to be virtual.
Note that if you implement this, the money will be captured at once too. Orders that cannot be captured (which shouldn’t happen, but anyway) will be set to “on-hold”.