Like what Lars said, but to clarify why...
By default, link aggregation is only one port per MAC address pair. All ports in a link-agg count as the same MAC address, so pretty much you'd be 1gbit anyway.
It's possible to configure link aggs to hash on layer 3, source + destination port pairs. Single threaded copies would still be limited to one link.
Then, we get into actual underlying bandwidth and packet forwarding rates. The A+ is pretty spectacular for consumer grade, but it *is* limited. Having to touch packets, generate hashes on headers, and then switch based on that is not part of the chipset, and the CPU would be saturated by that pretty quickly, long before you got a boost from it.
The best option would be to set the NAS to NIB, which is link agg where one port is active, and the other port is fallback. This gives you redundancy.
Also, you need to see what your NAS will actually push. If the NAS is not pretty high end, I think you'll have trouble saturating a gigabit link due to CPU limits. You'd need jumbo frames to really see good benefit, which should be a separate network, as jumbo + non-jumbo on the same subnet leads to all sorts of lag while things coordinate MTU.
Also, if it's just a mirror pair, or a raid5 of 8 or less disks, or if it's not SATA-III, or if it runs through a port multiplier, then I think you'll find the I/O limits will not go past gigabit anyway.
A test would be to put multiple IPs/Subnets and see...
Consumer grade routers don't support link aggregation. You need a managed switch for that to work. Netgear has a $75 option that should do the trick http://www.amazon.com/NETGEAR-ProSAFE-GS108T-Gigabit-1000Mbps/dp/B003KP8VSK/
Just make sure your NAS and the switch supports the same type of link aggregation, as there are a few different types - http://en.wikipedia.org/wiki/Link_aggregation#Driver_modes
Also note that even if you do this, as long as you only have a couple of PC's on the network, you won't see any real performance benefit. Also note that even if you have two network cards in your PC and think this will boost the speed of your network to 2Gbps, it won't as aggregation sadly doesn't work like that