if you don't have the funds for the flight then I doubt you will be able to petition for your bankruptcy unless you can persuade a family member or friend to represent you free of charge.
Whosoever were to represent you would need a Lasting Power of Attorney which costs approx £150 and can take a few months to arrange. As you will not be present the petition must be filed at The Royal Courts of Justice (High Court) in The Strand for which the fees are £507.
If you have nobody to represent you then there are firm's that will do this for you, the problem is their fees will very likely outweigh the return travel costs which you cannot afford.