Splitting a magnitude across multiple bins in an IFFT
Your frequency in term of bin number is approximately:

SignalF / binDelta = 110 / 86.1 = 1.28


So, for the positive frequency image :

w0 = pi * (0 - 1.28)
w1 = pi * (1 - 1.28)
w2 = pi * (2 - 1.28) = pi * 0.72
wx = pi * (x - 1.28) 
binmag(x) = sin(wx) / wx


Also, one needs more than 3 points to avoid windowing artifacts.

But the big problem with Sinc interpolation for any f near bin 0 (DC) is that the signal plus its complex conjugate mirror image at the nearby negative frequency -f both wrap across bin 0, and thus constructively or destructively interfere within all those nearby bins, depending on the phase of f measured relative to the center of the window.  See http://www.nicholson.com/rhn/dsp.html#4 for a more complete Sinc (or Dirichlet) interpolation formula.  A similar problem occurs for frequencies near bin N/2 for an IFFT of length N. This creates a problem with IFFT (re)synthesis of any fractional frequencies near DC or N/2.