Please help! RSS query… Optional excerpt over-ride?

Please please please someone help me. Even if it is just a simple – nope – it cant be done.

My WordPress is currently set so that RSS posts are published as an excerpt. You can view my feed here: http://www.thelineofbestfit.com/feed

Now – for my theme to work properly – I have to add an optional excerpt in each post to display on the home page. See what I mean here:

http://www.thelineofbestfit.com

the thing is – the optional excerpt ends up getting published to the feed when in an ideal world i’d love it if the reader instead could pick up to the ‘insert more tag’at the end of the first paragraph.

so, an example

instead of the RSS reader publishing this:
(optional excerpt)
Win tickets to this years most picturesque festival, the Hydro Connect Music Festival near Argyll in Scotland!

i’d want it to publish like this:
(up to ‘more-tag’)
We have three pairs of weekend with camping tickets to give away to Hydro Connect Music Festival which takes place in the fairytale grounds of Inveraray Castle in Argyll from Friday 29th – Sunday 31st August.

does that make sense?

if anyone could get back to me with ideas/suggestions/plug-ins etc please do so. i will be sooooo grateful!

thanks