How to pass extra options to OpenBSD's EFI boot loader with systemd-boot?

I have an extra systemd-boot entry for OpenBSD.

$ cat /boot/loader/entries/bsd.conf
title OpenBSD
efi /extra/bootx64.efi

It works and I manage to get into boot shell, The problem is that by default it tries to boot from hd0, I need it to boot from hd1, which I have to specify manually with

> set device hd1

I tried the following, but it didn't work

$ cat /boot/loader/entries/bsd.conf
title OpenBSD
efi /extra/bootx64.efi
options set device hd1a # it does not work

Is there a way to pass hd1 as a parameter to bootx64.efi, without typing it manually?