Help to vectorize THIS loop

[Macy]

I've got a large file of uniformly sampled time waveform, called sig.

I'd like to 'add' a small amount of aperture clock jitter to the data, call 
that sigwn. How to vectorize instead of doing with a loop?

The rms aperture jitter is less than 1/10,000 of the sample time, so I assumed 
I could easily use linear interpolation and 'slightly' adjust the magnitude of 
each data point. without distorting the effect too much, right?

The loop checks each data point and if the clock is faster, adds a little bit 
based upon the next data point, or if slower, adds a little bit based upon the 
previous data point. only changing slightly to reflect the linear slope to that 
value. 

Let SR = sample per second
clkjtr = clock jitter rms in seconds 

So I took the time as 
t=[1:hugenumber]; 
then added noise to the time window
tn=t+clkjtr*randn(1,hugenumber);

end points are a unique case so I can do those separately. 

sigwn=sig;
for i=2:hugenumber-1
  if ( tn(i)<t(i) )
   sigwn(i)=sig(i)-( sig(i)-sig(i-1) )*SR*( t(i)-tn)i) );
  else
   sigwn(i)=sig(i)+( sig(i+1)-sig(i) )*SR*( tn(i)-t)i) );
 endif
endfor

any slick ways to vectorize this?

like don't create tn, but rather create 
dtn=clkjtr*randn(1,hugenumber);

then make two lines, checking for 'sign' condition?
sigwn=sig;
sigwn(dtn<0)=sig(dtn<0)+ ??;
sigwn(dtn>0)=sig(dtn>0)+ ??;
except of course the END POINTS.
where I can only use 2:end-1 for these two lines.  
arrrgggg!
I don't see how to avoid the end point problem WITHOUT creating more huge sized 
variables, which may be ok.