Quote:
"We�ve run a flower shop for many years and have found that lilacs hold up much longer if you remove the leaves, crush the stems ends, and place them in a container of wood alcohol. Let them stand in a cool place, out of drafts, for about an hour (or a little longer if branches are large). Remove and put them in cold water in a refrigerator overnight.
One of the finest weddings we ever did was with lilacs (white) handled this way the day before. Even the bride�s bouquet was made of lilac blossoms and not a single spray of flowers wilted. The ways these lilacs inhaled alcohol was unbelievable. The branches absorbed almost all the alcohol. We�ve handled blossoms of mock orange, weigela, and apples this same way and with success.�
Source:
http://www.ramseyadagency.com/cfbook/cf.htm
Note: 'Wood alcohol' = Methyl alcohol = Methanol. I'm not sure where you could get it from but I suspect that any form of alcohol would give the same result. I'd try using methylated spirit (from any DIY store), which is ethyl alcohol with a small amount of methyl alcohol added to it.
Chris