Is there a possible way around this?
Mmh, should be no problem at all unless you are using an odd combination of framerates or are trying to enforce the old VP5 CoDec....
This animation is for a normal monitor that will be rotated 90 degrees, correct? You don't want 1080x1920, you want 1920x1080.
It's certainly possible to work in a 1080x1920 comp to make life easier on yourself, but eventually the video will be 1920x1080.
You'll need to find out if they're rotating the monitor clockwise or counterclockwise, nest your work in a 1920x1080 comp, and rotate the nested comp appropriately.
The digital signage sub-niche of the motion graphics industry may offer you some useful advice.
Non-square pixels are the death of most of us who produce for portrait displays.