You do not need a temp gun to break in an engine. If you don't want to do the temp cycling method, then there's really only one other method available to you, the 'old school' way...

Run the first tank on the starter box at factory settings. Let it cool (it won't have got very hot anyway) Start the second tank on the starter box, then lean it 1/8th of a turn, halfway through the second tank, lean it another 1/8th of a turn, and put it on the ground. Finish the second tank doing slow up and down runs. Let it cool again. Run three or four more tanks like that, leaning only if the engine is bogging so badly it stalls. If you do choose to lean it more, only 1/8th of a turn at a time. If after an adjustment there is no longer fuel spitting from the pipe, then richen it back up again until there is. You want a fair bit of spitting right up to the 6th or so tank. After the 5th/6th tank, you can start leaning it out more...you still don't need a temp gun, the spit test is adequate, just put a drop of spit on the engine head. If it jumps off, your too hot, if it just evaporates slowly, you can lean it a bit more, it should sizzle nicely and evaporate fast. It may not sound very scientific, but it works very well. After each run MAKE SURE you return the piston to bottom dead center as it cools, or you may stretch the liner.

Finally, don't tune to temperature, you may have a cool running engine, which means if you lean it out to get high temps (250+), you may not be supplying the engine with enough fuel to lubricate itself, this will result in permanent damage pretty quickly. If in doubt at ANY stage, get help from a local experienced nitro person. It is not worth destroying your egnine just because you are impatient.