I've tried my luck on Discord channel, I've received two answers:
a)There is no support of mouse for this version at all
b)Pressing power+b should make that left thumbstick will behave like d-pad, while right thumbstick should be functional as mouse
Sadly, I've tried option b and it didn't work in my case.
I guess that without update there is no way to use mouse. Is anyone by chance knows, who I could contact about update to this version of DosBox?