If the valve is seized and you are fed up with the 7K code you can temporarily disconnect the cables at the EXUP end as the servo will then be able to operate properly and will not generate the fault code, but you definitely should attempt to get it working again so you can appreciate the bike as it's meant to be.
In answer to your question about alternative valves I did a quick search and found these threads;
http://foc-u.co.uk/index.php/topic,18325...#msg211069
http://foc-u.co.uk/index.php/topic,19418...#msg224471
I guess temporarily you could blank off the valve housing and leave the assembly in some paraffin or repeatedly apply penetrating fluid to attempt to free it up. Be aware that it is quite easy to bend the valve which can cause it to stick as it rotates, you can straighten it out but this is a bit of trial and error.
In answer to your question about alternative valves I did a quick search and found these threads;
http://foc-u.co.uk/index.php/topic,18325...#msg211069
http://foc-u.co.uk/index.php/topic,19418...#msg224471
I guess temporarily you could blank off the valve housing and leave the assembly in some paraffin or repeatedly apply penetrating fluid to attempt to free it up. Be aware that it is quite easy to bend the valve which can cause it to stick as it rotates, you can straighten it out but this is a bit of trial and error.