I believe it's possible, although it isn't well-documented in the manuals. There's a "no chord" or "N.C." chord type that's recognized by most Yamaha arrangers, triggered by pressing three consecutive keys at the same time, or what the manuals refer to as "1-b2-2" (that is, the root, flatted second, and second).
The only wrinkle is that if you press three keys which are physically consecutive on the keyboard-- as opposed to being musically consecutive in terms of the twelve pitches of the chromatic scale-- the PSR-E models will usually interpret it as an attempt to trigger a minor seventh chord using the "easy-fingering" chord method.
Consequently, you typically need to shift one or two of the notes by an octave so the keyboard will still recognize that you're pressing the root, flatted second, and second notes of the chromatic scale but are trying to trigger the N.C. chord type rather than the minor seventh.
In terms of stretching your fingers, I find that the least awkward way to do this is to use your left pinky finger to press the C# key, and simultaneously use your left thumb to press the B and C keys which are an octave above.
You can also try pressing three physically-consecutive keys, as long as they don't fit the "easy-fingering" method of triggering a minor seventh-- that is, try pressing white-white-black, meaning B-C-C# or E-F-F#.