This is mostly a spinoff of the recent discussion about CP Italy: a scenario where Italy joins the CPs because the Entente powers attack first, so Italy is bound to the terms of the defensive Triple Alliance.
Your task is to devise the means by which this alternative sequence for the start of WWI occurs:
Brownie points if the war still starts about the assassination of Franz Ferdinand.
Russia or France declare war first to a Central Power.
Germany takes a defensive stance in the West.
Italy joins the CPs.
France invades Belgium or Switzerland.
Britain remains neutral at first, it may join the Entente later, if it can ever concoct a plausible justification for the British public, or more likely never at all, as it lacks a decent casus belli and unrest sooon explodes in Ireland.
Turkey and Bulgaria join the CPs.
Serbia and Romania join the Entente.
Japan joins the Entente if Britain does, the CP is Britain is neutral.
America remains neutral.
I'm aware that the key prerequisite of the scenario is Germany digging Plan Schliffen (realization of its logistical difficulties ? awareness that it may bring Britain in the war ?), so it does not need to beat Russia and France to the gun, it may let Russia or France look the aggressor, so Britain has not a casus belli and Italy is more tightly bound to the terms of the defensive alliance. But it is not perfectly clear to me how the diplomatic and strategic PoD would be realized in detail.