The dudes on
Mythbusters * still tested positive (faintly) 24 hours after initial ingestion.
Sorry.
A woman did win an extremely lucrative lawsuit against a company that refused to hire her following a hot urine result, so you may be able to make out well if you can prove it was JUST the poppy seeds.
* This is a link to the show's main page. They seem to have a few goodies upcoming — I'm particularly looking forward to "Exploding Toilet" but I didn't immediately find a link to this past Friday's show.