BizTalk mapping records into pairs - biztalk

Question

Using a BizTalk Map and wondering if there's a good way to do the following.
I need to map a received Invoice to a list of Orders. However each Order must contain only two line items (let's assume the Invoice has an even number).
This means that Invoice(1, 2, 3, 4) should map to Orders(Order (1, 2), Order (3, 4)).
Essentially, I need to create new parent elements when (index % 2 == 0).
Is there a functoid-only way of doing this?
XML example below:
<Invoice>
<Client>Client1</Client>
<Line>
<Code>1</Code>
<Price>$1.00</Price>
<Qty>1</Qty>
</Line>
<Line>
<Code>2</Code>
<Price>$2.00</Price>
<Qty>2</Qty>
</Line>
<Line>
<Code>3</Code>
<Price>$3.00</Price>
<Qty>3</Qty>
</Line>
<Line>
<Code>4</Code>
<Price>$4.00</Price>
<Qty>4</Qty>
</Line>
</Invoice>
to
<Orders>
<Order>
<Client>Client1</Client>
<OrderItem>
<Code>1</Code>
<Qty>1</Qty>
</OrderItem>
<OrderItem>
<Code>2</Code>
<Qty>2</Qty>
</OrderItem>
</Order>
<Order>
<Client>Client1</Client>
<OrderItem>
<Code>3</Code>
<Qty>3</Qty>
</OrderItem>
<OrderItem>
<Code>4</Code>
<Qty>4</Qty>
</OrderItem>
</Order>
</Orders>
What I've tried:
Standard mapping: A single Order with all lines, as expected
Value Mapping to Client based on index % 2: Order per line (half have Client)
Table Looping (Gated to index % 2) + Extractor to Client: Order per line, only half lines
What I'm likely to end up doing:
XSLT
Or, C# manipulation after mapping

Answer 1

In the advanced functoids section of the toolbox look for the 'index' functoid.
Add a scripting functoid on the output.
Add C# code to check for the indexes you want to match.
You can switch output on and off by returning a boolean from the scripting functoid.