Well you could find the indices of all the nonzero rows for a matrix A as
idx = find(~all(A==0,2));
and then you can replicate rows from idx(1)+1:idx(2)-1 equal to A(idx(1),:) using repmat function in matlab.
There could be a better logic for this but right now the one that's coming to my mind is something like this,
for i = 1:length(idx)-1
A(idx(i)+1:idx(i+1)-1,:) = repmat(A(idx(i),:),length(idx(i)+1:idx(i+1)-1),1);
A(idx(end)+1:size(A,1),:) = repmat(A(idx(end),:),length(idx(end)+1:size(A,1)),1);
You can develop your own logic but this kind of works as well.