Hi Petr,
That's what ST4 autoguiding is. It sends corrections to your mount by emulating the button depress.
It should be quite straightforward depending on your model.
you might have to do some soldering to wire it to an RJ11/45 connector so the guide camera can connect to it. but once its done, it should work well.
if you don't have a guide camera with an ST4 port, you can get the shoestring astronomy webcam adaptors that provide an ST4 interface.
are you able to solder/understand/test simple circuits?
Please post some info about your mount with pics of your hand controller
this explains the mod for EQ3 mounts. you'll have to check if yours is similar.
http://www.store.shoestringastronomy.com/eq_mod.pdf
Cheers