Combine two manufacturer filters

[philip937]

Is it possible to combine two manufacture filter ids to show both manufacturers in the same listing?

For example I can filter
?sort=20a&filter_id=3
And
?sort=20a&filter_id=4

But can you do something like
?sort=20a&filter_id=3&filter_id=4

So that both show? The above doesn't work obviously but wanting to know if there is a correct way of doing the query to make it work?

Phil