How to add system libraries to flatpak app(for more input methods)?

Flatpak currently supports only fcitx and ibus as input method.
But there are a lot more input methods like nimf, uim, …

I use nimf or uim because ibus and fcitx have some problems with chromium browser engine.
But because flatpak does not support nimf or uim I have to give up flatpak or nimf/uim.

Is there any way to add nimf or uim libraries to flatpak apps by myself?
Or any plan to support other input methods?