and had to Wireshark the username and password from the supplied Sky equipment.
You didn't have to do that.
You can just use a generic username and password now.
Not even sure if that's needed now, I was sending a generic string in option61 but I just tried removing that and I still got an IP after restarting the router.
Three possibilities here
1) openwrt sends something in opt61 out the box
2) because my MAC is already learnt somewhere it let it though without the opt 61 param
3) Sky have finally dropped the requirement for opt61 and it's just standard DHCP now.
This was with an HH5 running openwrt on a NowTV FTTC line.