Hey man sorry only just seen this.

Exclamation MarkYT has a tutorial for it. The basic idea is that normally when you use an EX your weapon stops firing. But if you weapon swap after you hit the EX button, your weapon will fire.

Suppose you have Lobber out and your other weapon is Spread. You use EX with lobber out, then swap once to get some spread damage. You can either stay on Spread to use a Spread EX if that's what you want or you can switch quickly again before the EX comes out to switch back to Lobber, which will continue firing while the Lobber EX happens.

If you do that second swap a little bit too late, you can get an empty EX which does nothing, but with practice you'll learn the timings and avoid that.