Many Linux environments allow you to enter Unicode codepoints. On my machine, I:
1) key Control-Shift-U and release
2) type the hex for the character
3) press enter or space
The hex for Ω is 3A9. If your system works the same, you should see after each step:
1) u̲
2) u̲3̲a̲9̲
3) Ω