Hey Bud, can you tell us what kinds of drosera you're dealling with? Most are pretty sturdy, and don't mind some root disturbance (like capensis, for example), but there are some you really want to be careful with....
I've only ever repotted the sturdy kind (fear of failure, I guess
), but here's how I do it:
Dig the sucker up (take care not to really cream the roots). If it's in a pot, try to get a grip around it's base (you may need tweezers, depending on how big it is), turn the pot upside down and tease out medium. Hopefully it will retain the shap of the pot.
Since you doubt your medium, to clean the roots, gently swish the root ball around in a container of water. once you've done this, rinse with distilled, purified or rain water (you can use tap water for the swishing part).
Second: replanting. your mix (50/50 pete/perlite) sounds fine for most drosera. Using LFS at the bottom to plug the drainage wholes is cool. I don't know about the charcol, I've never tried it.
Now fill up the pot with your medium, and make a whole for the roots. Place roots in whole, fill in whole with more medium, lightly tamp it down. Done.
Look to more experience Drosera growers for replanting the more fragile species....This is how I handle my capensis, spatulata and alicaie.