Going around it would be a nightmare! I'd be willing to risk it.
I did see yer man on the tv once (tommy walshe) put in foundations for an extension and there was a sewer pipe crossing at right angles. He just put 2 blocks either side of it and on top and filled her up then with concrete.
In my case the pipe runs diagonally across, and its a garage not part of the house. (would a garage wall (cavity blocks) be a bit lighter than 4" block walls with a cavity?)