Been AFK for a while so I forgot to update the Bulgarian Teardrop thing...
I've found that it doesn't work anything like as well if you cook the chillis into the stew, and even adding a raw puree at table isn't much good either. Not much of the flavour survives prolonged heat or contact with oxygen.
I doubt that drying or pickling would work either.
The only thing that works really well is how I did it the first time (pure luck).
Take well-developed (heavier, thick walled) BTs while they are still green, remove the seeds and pith, chop into 2-3mm squares and mix into the dish at the last minute.
It's the fresh zesty flavour released as you chew them that really does the business.
BTs aren't that hot so start with about a level teaspoon of chopped chilli mixed into a portion to give the big 'lift' to the flavour without scaring anyone except the seriously wimpy who think a drop of tabasco sauce in a gallon of stew is unbearable.
I've also found my Bishop's Caps don't work either though this strain is notoriously variable (aka. Balloon etc.) so some others might work.
Cheers.