FX7500 and multiplexer

Hello,
My Company is writing app that uses FX7500 Rfid reader and multiplexer. We are controling multiplexer throught GPIO ports (state status looping), and we can get readings from correct antena input from muliplexer. The problem is we don't know from which multiplexer antena input tag is read, because tags are buffering and state status of GPIO has changed when ReadTagEvent occurred.
Is there any way to attach GPIO state status to tagData (when tag is seen) with LLRP or API3, so we can correctly pair tags with multiplexers antena ports ?
Best,
Lukasz