What you are looking for is QoS (quality of service), for an explanation see for example here:
http://kb.netgear.com/app/answers/de...es-performance. No idea whether your router supports QoS though.
'Splitting' the connection in the way you suggest would not work, because your problem is not speed but latency. Consider this (very wrong and incomplete) comparison: the connection is like a car which transports goods. It can transport large amount of baggage each time (this is basically the speed), but it takes time to make a trip (latency). Now your problem is that you want to send just a small bag (but do it on time), while the other person has a lot of stuff to move. So in the end the car is more likely to pick his stuff and you have to wait till the time they decide to pick yours (which can be a few trips). So what you actually want is for car to take care of your package first - this is exactly what QoS allows you to set up.
Good luck!