I don't have either of these devices personally, but it looks like a user on the Neptune Apex forum
posted about this topic. It's a bit complex because it looks like you have to tear apart a network cable and a 3.5mm audio cable.
I don't know where you live, but
Bulk Reef Supply sells these for about $12. If you are in the US or can otherwise receive shipments from Bulk Reef Supply, I would personally just buy one. But, I also understand the desire to DIY