From the Just-Dice database of debits and credits:

  Mon Jul 15 15:09:58 2013 {"amount":1300.155,"address":"manual debit","txid":"","eid":22234}
  Tue Jul 16 07:53:03 2013 {"amount":1300.155,"note":"manual credit","eid":23310}

ie. I debited his account late, after he had already lost the balance (taking his balance negative, in the hope he would deposit to clear the debt), and then later re-credited it after rolling back the bets.

So the amount in question is exactly 1300.155 BTC.

Edit: here's the transaction where I paid him out but didn't debit the database:

https://blockchain.info/tx/0aa67253b162c6ddae04bbc5b01a0283591a74288cdd1c2073a3181ec7e124da

1ChELp7ynrwpktFJvRgrBECWxWWg2Mxu72 - (Spent) 1,300.1549 BTC

That's 1300.155 BTC minus the standard tx fee of 0.0001 BTC.