Your best POD is the US or USSR putting reunification on hold a little longer till the East has something in place to match the Western electoral machine. (I still find that unlikely)
I think this wouldn't be sufficient. Reunification was not only popular in the West, but also in the East. I think the feelings of a large part of Eastern Germans is well put in the following slogan:
Kommt die D-Mark, bleiben wir, kommt sie nicht, geh'n wir zu ihr!
(If we get the Deutschmark, we'll stay. If we do not get it, we'll go and get it.)
The implicit threat of the users of this slogan therefore was that they want economic benefits West Germany was able to provide. And they wanted it immediately, Only reunification was able to provide these economic benefits in time. If reunification were delayed, millions would have used their new freedom of movement and resettled to Western Germany - what happened anyway IOTL.
Nevertheless, I think many more would have left Eastern Germany for the Western part if there were no early reunification. In particular, the younger and better-educated would have gone. Anybody could earn significantly more in Western Germany, there's no language barrier, you could buy whatever you wanted in the West, everything is so modern and free, housing is better, polution is significantly less...
Now, to avoid this mass-exodus of the most productive part of the population of Eastern Germany, your only chance is that West Germany denies them entry. And that would be political suicide for any politician who proposed it - Western or Eastern - as it essentially rebuilds the wall.