Sustain a Spell / Activation in Battle Form?

My sorcerer player had an interesting question: animal form is two actions, meaning you can begin the round by, say, Sustaining dancing lights to provide the party vision and then become a bear. The question is whether, in this hypothetical scenario, the sorcerer-turned-bear could continue to sustain dancing lights (or, let's be honest, flaming sphere).

While a bear, you are under the effects of the polymorph trait, which specifies that you cannot cast spells (or activate items), speak, or usually engage with manipulate actions that require hands. You can use the Dismiss action, however, which shares the same traits as Sustain a Spell.

My initial thought is yes. Polymorph even says "if there's any doubt about whether you can use an action, the GM decides"! But I was curious what people thought / if there was a definitive answer. "Yes" is an acceptable answer for my table, but I always feel like I'm missing something when my players ask a question and I can't find an answer!

I would allow it. Sustain a Spell only has the Concentrate trait, and nothing about polymorph type spells preclude you from performing Concentrate actions.

The one exception I could find would be the Critical Failure outcome of Baleful Polymorph, as you are transformed "body and mind" into the creature. In that case, I would treat any magical effects the character had as though they had died.