Simple digits only input method (like t9 for cellphones) for fcitx.
use 2-9 to input, 1 for backspace, and press 0 will step into state where user can choose candidates. At this state, use 8 for page up, 9 for page down, and 1-7 are used to select specific candidate. after selection, we go back to normal mode where you begin to input another pinyin.