Have Alans less integrated into roman dispositives and armies in Gaul could help.
While staying as allies of Romans, they could devellop their own kingdoms more quickly.
It would need as well to prevent the separation between Loire and Rhone Alan kingdoms, as well the departure of some in Africa and Spain following the Vandals would be really helping.
The lack of organisation and clear leadership really helped to these divisions : having an ethnogenesis beginning before 400's would be necessary.
Having a Gallic Alania between both rivers (roughly modern Bourgogne, Lyonnais and Berry is doable.
However, I can't see them standing eternally again more organised and disciplined peoples. At best they would be romanized and christianized before being conquered making the region being distinct (as OTL merovingian Burgundy).
At worst, they will end as Rhenish Franks, and not having a big impact.