Thread Subject: Inserting elements in a vector

I have a vector v1 of L1 elements. I need to insert elements of
another vector v2 of L2 elements (L2<L1) into known positions of v1.

What is the fastest way to do this? Right now I preallocate L1+L2
elements for v1 and for every position I have to insert a sample, I
right-shift all the elements of v1 to the right of that position and
then insert the value. This is taking a long time.

somdeb:
<SNIP vec acrobatics...

one of the many solutions

% the data
     v=1:10;
     w=[-10,-20,-30];
     pos=[2,6,7];
% the engine
     tf=false(1,numel(v)+numel(w));
     r=double(tf);
     tf(pos)=true;
     r(tf)=w;
     r(~tf)=v;
% the result
     r

us