It might be possible.
06FD00 06FD0F PTR N "Pointers to Overworld data (local, first at 06FD10)" 2004.06.21
06FF20 06FF3F PTR N Pointers to Overworld maps (first at 066A39) 2004.06.21
06FFA0 06FFBF PTR N Pointers to Overworld music transition data (first at 06DA76) 2004.08.23
06FFC0 06FFDF PTR N Pointers to Overworld exit data (first at 062411) 2004.06.21
06FFE0 06FFFF PTR N Pointers to Overworld Events (first at 038B6C) 2004.06.21
If all of those pointers were relocated and had an extra entry, you should be able to stick in one more overworld, but you'd need to juggle things to edit it in Temporal Flux.