How can I compute bcrypt hash with less than 16 (2^4) rounds on Linux?

How can I compute bcrypt hash with less than 16 rounds (cost factor of 4 = 2^4 = 16 rounds) on Linux? This is the same question as https://unix.stackexchange.com/questions/307994/compute-bcrypt-hash-from-command-line , but requiring a cost factor of 1 to 3. All of the answers there only allow a cost factor of 4 or higher. This is what they say:

> htpasswd -bnBC 3 "" Y
htpasswd: Unable to encode with bcrypt: Invalid argument

For https://bcrypt-generator.com/ , setting cost to 3 or less computes a hash using a cost factor of 4 ($2a$04$Gtm/m3uLxfxcezWRLcVLBuUTNbrSse/.XsBK16WBN5u37Cl88kaFy) For https://www.browserling.com/tools/bcrypt , Rounds exceded maximum (30)!.