BLF on Digum D50 for two line on two diferent server

I have Digium D50 with defined 2 line, 1 line is on server A, and line 2 is on server B. I have BLF for same extension on server A and thats work, but BLF does not work for extension on Server B although is line 2 from server B. Is it posible to use BLF on this scenario?