As I understand it, there never was an "East First" strategy that tilted the scales like the OTL one against France. At least not when France and Russia where concerned.
What I read as AH "East First" is more of a balanced one that uses the German advantages, ie. inner lines and counter attack, to achive its goals. At least that is what I got from the discussions and everything.
So to go there, you probably have to rise the stakes in the West. Like Britain being very clear about Belgium and also having more army to enforce it. Butterflies here galore... but you could get it. Or the Germans realize that the Russians may be faster in mobilisation and do something about it. For this you probably have to reshuffle the Generalstab as Moltke Jr. was very set in his plans.
So in all it Imo would not be that hard to construct a chain of events that lead to an "East First" that is more defensive in the beginning and counters the expected Franco-Russian offensives. How that will play out in the end, only the author would know. As it also needs a clear picture on how others react.
On the other hand, a tilting of resources towards Russia as on the OTL scale against France, Imo, is impossible as too much value was in the western parts of Germany that France could reach in short order. So the Germans will have to put more weight into the west even when they would decide to go East as a priority.