MATLAB: How to efficiently zero-pad a matrix with varying lengths

concatenationMATLABvectorizationzero-pad

Here's my modified code after integrating advice from the 3 answers below (and if I could I would accept all three of the answers, I only accepted the first because it was the first. There should be some way to accept multiple answers because each one was helpful!):
num_points = 100 * 100 * 75;
for i = 1:num_points
    % zero_pad_length only changes every 3 "s"
    zero_pad = repmat(zero_pad_length(:,i), 1, 3)';
    offset_trace(1:end-zero_pad,:) = trace_to_offset(zero_pad+1:end,:);
    results(i) = max(prod(offset_trace));
    offset_trace(:) = 0;
end
It's 50% faster than it was before. Thanks everyone for your help.
ORIGINAL QUESTION: I've been working at this for a bit, and I'm not really sure where to go from here. The basic structure of what I want to do is (results and offset_trace are preallocated with zeros()):
for i = 1:100
    for j = 1:100
        for k = 1:75
            for s = 1:30
                % zero-pad a vector with different lengths of zeros  
                offset_trace(s,:) =       [trace_to_offset(s,1+zero_pad_length(s,i,j,k):end) zeros(1,zero_pad_length(s,i,j,k))];
            end
            % then take the max of its product 
            results(i,j,k) = max(prod(offset_trace));
        end
    end
end
I don't see any way to vectorize the first three for loops (those loop over a 3D grid) because for each point of my grid there's a different pad_length for each of the 30 different rows of trace_to_offset.
I've tried to vectorize the for loop over s with:
str_to_eval = sprintf('[trace_to_offset(%i,1+zero_pad_length(%i,i,j,k):end) zeros(1,zero_pad_length(%i,i,j,k))],', stats');
offset_trace = eval(['vertcat(' str_to_eval(1:end-1) ')']);
but it takes exactly as much time to run as the first option. Are there any other solutions that could help me speed up this zero-padding?
Or even better, if it's possible to vectorize the first 3 for loops?
EDIT: For the comments belows and stat should have been "s"! Sorry for the mistakes.
EDIT_2: I've included my modified code that integrates the 3 answers below. Thanks to everyone for your help!

Best Answer

Pre-allocation:
results = zeros(100, 100, 75);
offset_trace = zeros();
c = trace_to_offset(stat, :);
n = length(c);
for i = 1:100
   for j = 1:100
      for k = 1:75
          d = zero_pad_length(:,i,j,k);
          for s = 1:30
              % Fill in initial part, equivalent to zero padding:
              e = 1 + d(s);
              offset_trace(s, 1:n-e+1) = c(e:n);
          end
          % then take the max of its product 
          results(i,j,k) = max(prod(offset_trace));
      end
   end
end
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