VBF production of t t~ w+ w- exclude diagrams

Hi, I want to choose a subset of diagrams from the ones of this process
> generate mu+ mu- > vm vm~ t t~ w- w+ QCD=0 / mu+ vm
this process has 496 and I want only the 216 that consists of VBF, that are the same that come from the process
> generate w+ w- > t t~ w+ w-.
Because i see that the undesired one have at least 3 s-channels is there a way to remove the first 280 by imposng that i do not want more than two s-channels in the proces?
More in general when i have a lot of diagrams and im only interested in VBF processes do i always need to manually exclude diagrams?
Thank in advance.