Neat solutions provided, but there are probably more straight forward ways to solve the original problem. One of these might help.
In:= s=0; Apply[Do[s+=i^i,{i,##}]&,Hold[1,12,3]]; s
Out[75]= 10000823800
In:= r=Hold[s=0;{1,12,3};s];
Part[r,1,2,0]=(Do[s+=i^i,{i,##}]&); ReleaseHold[r]
Out= 10000823800
In:= s=0; Apply[Do[s+=i^i,{i,##}]&,Hold[1,12,3]]; s Out[75]= 10000823800 In:= r=Hold[s=0;{1,12,3};s]; Part[r,1,2,0]=(Do[s+=i^i,{i,##}]&); ReleaseHold[r] Out= 10000823800