You can do this in the current release:
1) Add the persistent damage effect as PERS: 1d6 bleed - changes every round, it's not static.
2) Or add another damage entry to the weapon with a d6 damage and type of "persistent, bleed" - this will apply the PERS: 1d6 bleed when damage is rolled on a target.
The critical 1d12 persistent bleed isn't handled at present, so that will have to be manually adjusted by the GM after it's been applied.