Manually adding an Elemental Focus bonus spell?

[MagisterMundi]

I have an Arcanist Elemental Master with Fire as his focus. For those who don't know what that entails, basically he gets bonus prepared spells provided they have the "Fire" descriptor, along with some elementally relevant modifications to Arcanist Exploits.

Anyway, here's my issue: I just hit level 4 with him, which means I finally have access to Level 2 Spells. I'd like to add the Molten Orb spell as his Elemental Master bonus prepared spell, but unfortunately Hero Lab isn't displaying it as an option. I'm assuming this is because it's both an Earth AND a Fire Elemental spell and because it lists Earth first, but as far as I can tell, it should still be a valid choice, since the Elemental Master bonus spell function only specifies that it must have the appropriate Elemental descriptor, not that it must ONLY have the appropriate Elemental descriptor and nothing else.

With that said, is there a way to manually add Molten Orb to the list of Elemental Master bonus spells? If so, how would I do that? Thanks in advance to anyone who can help!