Thanks for your suggestion, however, sorry, but please note this is not possible.
In the decimal system, there are ONLY 10 digits - 0 to 9.
(we use 1 to 9 in our pattern Login/unlock screen)
So, there is no way to have any other grid larger than 3x3.

Regarding hiding exact path, there is an easy way! -->
The pattern is actually digits. You should be able to figure out the digits, they go like this:
1 2 3
4 5 6
7 8 9
So, if your pattern is first row first dot, first row second dot, second row second dot, the digits are 125.
If your pattern is S-shaped, the digits are 321456987. If it is Z-shaped, then they are 1235789/etc.
So, if you enter the digits that correspond to your pattern as the TEXT password, you can use that to avoid getting your pattern seen, and still use pattern login when you are alone/etc.

RE pattern security:
Pattern is a bit less secure as the combinations are less, but we had a mathematician run some tests, and he said you should be fine if using a decently complex pattern.

also make it 'invisible' path please - it's visible from miles away in public :-(