I'm really pleased for you and your son although sad that you have had little choice and chosen a route you may find very difficult.
Regarding bursaries, as your son is not academic the only way they will probably consider offering you one is if they see him as an asset to the school. Of course all children are assets to the school because they shape the ethos and culture but you know what I mean. So encourage him to be active in all areas - plays, music, CCF, community service for the school - and good effort and behaviour are a must.If he is an active member of the school then they would feel the loss of him not being there so there is more chance they would offer you a bursary. Obviously he doesn't need any pressure and no child is a saint but treating him like an adult and giving him these responsibilities should help him rise to the challenge. If he is particularly strong in a sport or instrument that he enjoys then give him opportunities to advance as schools always love to boast about such and such a pupil representing their school at county level etc.
If you have time, which given your circumstances must be difficult, try and get involved in the school. Be on PTA's or fundraising commities and try and turn up to lots of events as this will show the school that you are interested in supporting them and in turn they may support you financially.
Keep us all posted on how he is getting on!