No cross pollination is required for lilacs. If sited and planted correctly, a single plant will thrive and bloom just fine on its own.

Yes, clematis can be propagated from cuttings however, it is much easier to get them started by layering.

Another idea is taking a young shoot from the original shrub.

Propagating lilacs

Are you wanting to save seeds from the lilacs -- I can't think of another reason pollination would be needed. Pollination is fertilization of the flower and is not required for the plant to produce flowers.

Also recommend layering, or even dividing, the clematis.