I think you'll get a non-trivial amount of people voting for Binface either a) because you don't care about politics & think it's funny b) as "anyone but Farage" c) to treat it as a by-election because they think Binface won't take his seat and it'll trigger the 'real byelection' with their preferred party instead.
According to the bookies, Binface is currently 8/1 to win (about 11% probability), and Farage 1/8 (about 89%), with the rest of the candidates nowhere. There's probably something Bayesian you could do to estimate the probability of various margins from that, but it's going to be uncomfortable for Farage no matter what - winning over Binface by an embarassingly small margin will not enhance his image, particularly if there is going to be another byelection called soon after with the financial issue continuing to be in the spotlight. The only way this works out favourably for Farage is if he scores a crushing victory over Binface with an increased voter share relative to his previous election result, and I think the odds of that are slim.
[0] https://en.wikipedia.org/wiki/RRS_Sir_David_Attenborough#Nam...