conditional clearances...
TOGA,
Great point! If the ATCO used your exact wording, it is non-standard phraseologie. Conditional line-up clearances are usually not a problem as long as they are given very specifically and according to ICAO phraseologie. In this case it should have been... Callsign XX, B E H I N D landing Airbus A330 (3 miles final), line up RWY 12L and wait B E H I N D. If this clearance is clearly read back then there should not be an issue at all.
Not at all do I want to say that I always only use standard phraseologie whilst working, however there are certain situations where it is of utmost importance that one does and such a situation includes clearances onto RWYs etc.
I'd be interested in what others have to say about this, but my experience has definately proven exactly this.
Cheers and take care
HB-UAE