for a sphere you can try OrientOnSrf, or FlowAlongSrf which you can also use your tube with. here you need the unrolled surface as a base surface. use UnrollSrf on your irregular surface and lay down your sphere or tube at the position you want it to be on the initial surface. uncheck rigid for the tube and it will flow directly over the surface without penetrating it. for an irregular pipe it works similar but you have to see that it does not penetrate the unrolled surface.
for a tube running over a tube i would suggest to take the curve for the pipe and elevate it to the center of its radius on the unrolled surface and use FlowAlongSrf with this curve and pipe then with history switched on which gives you the option to move the points manually till it fits.
in case you want the tube exactly on top of the tube you could elevate the curve and again use FlowAlongSrf and piping the curve again. flowing the ready tube unfortunately distorts it pretty well so thats the only way to go.