Override hostname in especific dhcp-client

Hello.. I have severals WANs whit DHCP on my mikrotik router and i need to every one of them inform to my ISP a diferent hostname, the variable $(HOSTNAME) is global, and i try to do it by script but i cant find how to set a specific hostname for independent interface, is this possible on mikrotik?

Each dhcp client allows to set own options (on Advanced tab), so just create another option with different hostname and use it.