There maybe some download manger software that you can restrict to only use a certain IP address. I do that with some dedicated game server software. So it is forced to used the network card with that IP.
But it will not help at all, even if you have like supper fast internet 100Mbps+ wouldn't even do it because your connection to your router will all way be faster then your connection to the internet. (I am sure somewhere in the world there is an exception to this)
It would sorta be like having 1 10 lain road (Wired LAN) and 1 4 Lain road (wireless LAN) merge together in to a 2 lain dirt road (internet connection).
My advice is use the Wireless when you are moving around and use the Wired connection when your staying put.