I do not have any experience, but there is an excellent description of lettuce pollination in an appendix of "Breed Your Own Vegetable Varieties" by Carol Deppe (I have the original edition, but I believe the same appendix is in the 2nd edition.)

Since you may not have it on hand I'll give a brief summary of what it says:

Lettuce - Strong inbreeder. Does not display inbreeding depression. Very little crossing between plants without intervention.

All florets open on same day (made up of tiny perfect florets). Flowers open, pollen released, stigma becomes receptive and fertilized within a few hours. Each floret produces 1 seed. Anthers fused into tube around style. Inner side of tube shed pollen onto style as it emerges.

Can be difficult to cross. Wash off pollen after style emerges, but before the lobes of the style curl outward. Use a fine mist of water on entire flower. More than one washing is helpful.

Individual florets can be emasculated by hand. Tube/code of anthers removed early on the morning of flowering --- difficult to do - florets are delicate.