Oh, there's a million ways to do it. Just get away from everything having to be "an event" or "the biggest threat to the universe ever (again)". It's a challenge, but that can make things interesting. You have to have some story you want to tell first, that's the hard bit.
I object to the whole idea of bringing back Davros after Genesis since it ruins that moment where Davros truly realizes what he's created. But that ship has sailed I guess.
But if I HAD to do it:
The obvious: Davros' backstory. It would be lame to have the Doctor meet Davros before Genesis, so you'd have to arrange things such that they don't meet. But I still don't like the idea of locking down the character too much. Maybe have a Dalek retell (with visuals for us) his origin to make some point as a story-within-a-story? That way there's wriggle room later i.e. the Daleks aren't entirely right about their own history, or misinterpret what they have. It's hard to believe we still don't know how Davros ended up like he is. Could have been as boring as a car accident in the Kaled City for all we know!
Why this is worth telling? Yes, it could be pure fanwank BUT the Resurrection Of The Daleks novelization actually did this in about a page and made it so compelling I'll never forget it. Basically, his lab was shelled and his peers left him alone to wake up with a button that would euthanize himself if he couldn't handle it. He woke up, considered pressing it but twisted his mind to become the Davros we know instead, with a vision unbound by weaknesses of the flesh and spirit for his people.
Non-origin stories are tougher, especially given how he's been overused. Journey's End was actually on to something there - having him being used for research by the Dalek leadership, but secretly desperate to take control. You could spin that out on an ongoing basis, highlighting the irony of his situation and his need to control his "perfect" creation i.e. you'd think he be happy for them? He did make them to be "superior" than humans including himself.
Or, stick with Genesis and have him (rightly) rejected by the Daleks as an inferior (he's just an injured human after all) and an independent agent. He could re-tell his own origin! I could see him being forced to come up with anti-Dalek biological weapons, which would leave the Doctor an interesting dillema i.e. who's the bad guy here? The Doctor's overthrown whole governments for less in the past ...