This is using “Super” instead of “Alt”. If you want to use the latter you only need to replace all “Super” instances with “Tab”.
#!/bin/bash
# Related discussion:
# https://github.com/davatorium/rofi/issues/38
xdotool search --sync --syncsleep 50 --limit 1 --class Rofi keyup --delay 0 Tab key --delay 0 Tab keyup --delay 0 Super_L keydown --delay 0 Super_L&
rofi \
-show windowcd -modi windowcd -window-format " {t}" -show-icons \
-kb-cancel "Super+Escape,Escape" \
-kb-accept-entry "!Super-Tab,!Super_L,!Super+Super_L,Return"\
-kb-row-down "Super+Tab,Super+Down,Down" \
-kb-row-up "Super+Shift+Tab,Super+Up,Up"&
sleep 0.1 &&
xdotool key Tab