It all depends on the style of catch can you decide to go with. If you go with something like this then you could plug that fitting. If you go with one of these, which is more like the filter you are asking about, you would plumb that line back in the throttle body area to keep a source of vacuum. One other idea is to run a Vacuum Pump which in some cases actually frees up some ponies by relieving the pressure that builds up underneath the pistons. You would also need the catch can with the vacuum pump though. Plus they help a lot with oil leaks.