It is very difficult to fully use the kit/bundle pricing module when the margin has to be fixed within the bundle itself. You should be able to have the option to use the component item margins.

Example.

Item 1 - £1 plus 100% margin (normally 100%) = £2
Item 2 - £1 plus 100% margin (normally 200%) = £2
Total £4 (lost margin is £1)

Item 1 - £1 plus 100% margin (normally 100%) = £2
Item 2 - £1 plus 200% margin (normally 200%) = £3
Total £5 (full margin is achieved)

Discounts for bundling can still then be achieved in pricing profiles.