You might be able to manage an AM4 build based on the 5600 but you wouldn't be able to buy a chunk of the stuff via OCUK unfortunately, that said there's really not much between them tbh unless you were hoping to grab a second hand 5700X3D down the line.
If you have Members Market access via this forum you might have some luck putting a request in for a bundle, I've seen a bunch of AM4 related parts go for pretty cheap over the past few weeks.