ain ma'avirin al ha'mitzvos - Avnei Nezer's chiddush in when to build your sukkah

The against (Meg 6b) writes that when there is a double Adar, according to R' Eliezer bar Yosi the megillah is read in the first Adar because of the principle of  דְּאֵין מַעֲבִירִין עַל הַמִּצְוֹת.  When you have one continuous block of time and can do the mitzvah earlier or later within that same block, there is a din of zerizus to do it earlier, but that's not a game breaker.  In his case, it's not a contiguous block of time.  There are days in between 14 Adar I and 14 Adar II when the megillah cannot be read.  Therefore, we come on to the principle of אֵין מַעֲבִירִין עַל הַמִּצְוֹת. 

Based on this gemara the Avnei Nezer (OC 459)  has a chiddush din that when there is a shabbos in between Y"K and Sukkos, a person must build his sukkah before shabbos.  You cannot build the sukkah on shabbos, so we treat the days before shabbos and days after as two separate time periods and apply the rule of אֵין מַעֲבִירִין עַל הַמִּצְוֹת.

Is that really true?  The gemara (MK 9a) writes that Shlomo haMelech made a celebration for chanukas Beis haMikdash before Sukkot so as to avoid the problem of מְעָרְבִין שִׂמְחָה בְּשִׂמְחָה.  That year they did not fast on Y"K because of this party for chanukas ha'Bays. The gemara asks: maybe Shlomo just happened to complete the job before Sukkos and that's why he made the celebration then?  How do we know it's because of the issue of מְעָרְבִין שִׂמְחָה בְּשִׂמְחָה?  Answers the gemara: if מְעָרְבִין שִׂמְחָה בְּשִׂמְחָה was not an issue Shlomo would have left a small part unfinished and timed the completion for Sukkos rather than schedule the celebration on Y"K.  (This topic comes up with regards to whether one dan delay a siyum until the 9 days.)

 

According to the Avnei Nezer, if in theory the Mikdash could have been completed either before Y"K or after Y"K, and obviously it could not be built on Y"K itself, wouldn't delaying the completion until after Y"K be a problem of ְאֵין מַעֲבִירִין עַל הַמִּצְוֹת, just like delaying building the sukkah? 

 

See more here.  The more more fundamental argument against the Avnei Nezer is that not reading megillah in the intervening days between Adar I and Adar II is a din in megillah; not building sukkah on shabbos is not a din in sukkah, it's just an extraneous problem of melacha on shabbos that gets in the way.