Splitting is a good move. As is looking to go via London if you are going from the SW.

e.g. for my 2011 outward to Mallaig, after 2 hours on the Trainline I jiggled times and split my journey from Exeter to Mallaig thus:
1 Exeter Paddington
2 Paddington Euston
3 Euston Glasgow
4 Glasgow Fort William
5 Fort William Mallaig

- compared to choosing just Exeter to Mallaig (to end up on the same final train) I saved just over £100 ! (Had to start 3 hours earlier though)

On the return journey Montrose - London(somehwere!) - walked 1/2mile over to Waterloo - Exeter - saved me £60 compared to a direct ticket to Exeter.