Schempp-Hirth Discus-2cT - which is still in production. It has a 2-cylinder 2-stroke Solo 2350 engine with a 5-bladed folding propeller. With a full tank of 13 litres of AVGAS / 2-stroke oil mix it has, in still air, a range of up to 200 nm without reserve.
The same glider is also available with a 'FES' Front - Electric - Sustainer motor. They have become popular because with the electric motor and prop in the nose it is a single lever operation for instant power - the drawback is battery capacity. Experience shows that trying to climb away gives very limited range - but may get you to another thermal - alternatively cruising at low level will get you further - but the range is probably in the order of 40 nm. There have been a few battery fires - with EASA banning there use in some gliders for a while - but I believe that the cause was identified and all restrictions now removed.
A small number of gliders have a gas turbine motor - these jet engines are small and lightweight, erect quickly, and the starting is pretty well full automated. Run on Avtur - but fuel consumption is high so range probable around 100 nm. But they do cruise under power at a good speed! You can hear them coming.

Right now petrol engines have greatest range - but most complex management. Improvements are being made to the petrol engine control systems to automate as much as possible and electric starters are now starting to be offered.

Since the objective is to get the prop to turn and windmill,it would be prudent to leave the magnetos `off`,to prevent an overspeed if diving,then turn back `on` after recovery. I would have thought that ,with the throttle closed,there would be minimal airflow into the cylinders,but at speed,if the throttle is quickly opened,there maybe sufficient`push` on a piston to turn the engine..`.However,I expect `DAR` may like to subject his 152 to some definitive restart trials...!!
Slight thread drift..I used to teach student t-ps and ftes at a civlian t-p school,at the spinning phase in a CAP-10 ,that we would initially do a couple of spins,in both directions,with the prop stopped.this should demonstrate the true spin characteristics of the aircraft.This was then followed by spins with the engine at idle,where one could see that most prop-engined aircraft have different spin characteristics due to engine power and prop rotation...
Perhaps DAR could try this ,feathering a PT-6 on a `Caravan....?

I've feathered the PT-6 on Caravan, DHC-6, and DC-3T. It works fine, and the engine runs happily at idle while the prop luffs at only a couple of RPM. However, great care is required bringing it out of feather, as it is easy to surge and overspeed. Handled gently, it's fine, but too quick hands will be expensive and damaging. The Caravan glides very much better prop feathered - like a push from behind as it goes in to feather!

One of my first instructors in a C150 told me to carry out a PFL to the runway, which I did.
On finals he asked me if I was confident of making the runaway. I said I was. He leaned over, turned off the mags, took out the ignition key and put it in the top pocket of his jacket!

Used to do much the same at least once with each student when I was instructing in 3 axis microlights. It was probably frowned upon by the BMAA but I felt it was important to show students that the aircraft kept flying even if the engine stopped, particularly in those days when most microlights had two stroke engines which were more likely to stop than typical light aircraft engines at the time.

Indeed the philosophy in microlight training in those days was this is what you do WHEN the engine stops, not IF!

(Maybe it still is.}

:) It certainly was for me, even if almost all of my training was behind a 4-stroke 912-er. I still have a deeply embedded habit of ever always looking around for the best field nearby for an emergency landing - if it doesn't help, it never hurts.