If my memory serves me correctly, windows has an option for 'mouse keys' (that would be a literal translation from Dutch, I'm not sure what it is in the English version). The '5' key on your numeric keypad will then act as a single left mouse button press, the '+' key as a double left mouse button press. Combining these buttons would at the very least allow you to input enough button presses per second.
If you've already tried that and the problem is with the game not recognising enough button presses per second, I suggest you try what Tommy suggested and turn all settings down as low as you possibly can for this segment only.
If all else fails, I don't think there is a 'console' that allows you to artificially skip this fight/kill the Kayran. However, you could upload your savegame and ask fellow forum members to complete just this part for you. You would miss a small part of the game, but at least you would get beyond chapter I. (I personally don't have a TW2 install on my PC at the moment, but I'm sure that there are forumites here prepared to help you)