Hi delyx,
My response comes later, but still I hope this will help.
The standard Stop-Loss settings will not suit you in this case, exactly because of the reasons you outlined.
What I'd suggest is turning them off and adding a dedicated trigger that would "match unmatched bets" with a specific price range. This way you tell the trigger to apply the action only to the bets within the price range you set, so the ones with prices higher than, let's say, 100 will not get matched.
However, to be on the safe side I would also include a trigger that cancels all unmatched bets after the matching trigger has worked, in case a fraction matched at 1000 is still there in the market.
See an example attached. To edit the price range, click on the "More options" link. I based the "match bets" trigger on the condition that it kicks in after a certain time has passed since the bet was placed, but you can replace it with your own conditions or add more.