Yeah remember I did the whole disabling of mid-race voting before back in the STCC days and it caused no end of problems under loads of situations I hadnt predicted, the server must in all circumstances be restartable somehow (my system didnt allow for it in some circumstances and it back fired).
X-System handling the voting for it might be the best way. With X-League on its way this might be an idea worth spending the time on, it's not actually that major provided there is always a way to bring about a restart.
Send a message when somebody tries to vote telling them to use the $r option or some such, and cancel all LFS restart votes.
$r[edflag] menu allows players in race to toggle a yes/no button selection with a simple - bottom of screen - interface that doesnt interfere too much with whats onscreen.
Optional $marshall menu shows players in race, who's vote counts, who's doesnt, and vote summary of how much more is needed to achieve a restart.
Perhaps scoring players based on race contribution to achieve a restart, 5pts for leader, 4pts for podium, 3pts for lead lap, 1pt for in race at start but retired.
The system should disable itself and allow LFS to handle restarting if there are less than 4 people (who started the race) driving on the server - thus during times of low operational density the LFS system kicks in, preventing all many of odd circumstances.