I came up with a good approximation on my Nord Stage by layering two piano samples without reverb and applying a different chorus effect to each. I could've done better with a different choice of piano sample (but can't fit any more piano samples on my Nord besides the huge grand I have); the point is that your standard "honky-tonk" piano sound is often caused by the piano being out of tune, and even having the individual strings for a note being out of tune with each other.
So, if you have a good upright piano sound, turn on some chorus and you should be pretty happy.
I also found a good piano program for the Korg TR/Triton series that just uses the onboard ROM and effects. If you have a Triton series keyboard, let me know and I'll send you a PCG of the sound.