Knowing what an improvement the shortshifter was in Arno's Elise, I also wanted one. After some searching I found a good option, that wasn't too expensive and only modified the forward/backward throw and not left to right. It is made by Gema Motorsport and costs EUR 79,00 excluding shipping.
After 1,5 weeks it arrived, including a German manual.

Fortunatly Arno was available to help me putting it in, otherwise it probably wouldn't have worked. Looking back the procedure it actually wasn't too hard, you just have to know how much force you can use.
Before we started I made a small video of the shifting mechanism moving with the original levers. The part you see moving is the part that is going to be replaced.

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First you have to remove the two cables that go to the gear leaver. You need some leverage to do this, using for example a spanner.

The part you're going to exchange is held in place by a small pin. This pin was a major headache to get out. After trying different methods we went with the "Use more force" option. Taking a pin drift, mounting a socket on that plus some extentions, you can use a hammer to actually knock it down. It might be easier to remove the water reservoir from the holder.

Put the pin drift on the pin.

Get a BIG hammer and bang it out.

This is the little basterd.

It has a kind of spring mechanism, can be very tight.

Another tip is using some penetrating oil on the pin. Give it enough time though to crawl between the hole and the pin.

Next you need to take the other part of the gearbox control axis. It is held in place by a metal ring and a plastic washer. It is very handy to have a mirror, so you actually have an idea of what you have to do.

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After a lot of fidling you're left with these:

One metal ring...

and one plastic ring.

You'll then be able to take out the first lever.

The first lever that is going to be reused.

It's getting emptier.

Then you can take out the second lever, including the rubber bushing. Save the bushing, you need it for the replacement lever!

The second lever...

One empty shaft.

When you put the two levers next to eachother, you can see the big difference. Not only is the replacement it shorter, but it's also lighter. The extra "wings" are probably to dampen vibration when using the gearbox on an Astra or Zafira. Doesn't seem to be very usefull on the Speedster, I can't notice any difference in vibration.

It's only a bit smaller :)

The difference in length for the gear change (35%).

Before putting everything back, all components should be greased up.

Finally, put the two levers back.

Lock the new lever tight using the bolt (no more irritating pins).

Put the second lever back with the two rings.

Then you hook up the two cables again and you're ready to go! This is how it looks with 35% reduction in place.

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The result is pretty good. The throw of the gear lever is shorter, but not too much . Gear change has more feel to it and is a lot quicker. This setup suits the car much better.