Hey,
I was looking into doing this myself at the end of my current grow.
I think the idea is to do a flush and then let the soil dry out for the last time. When the pots are dry/light you add the flavoured 'extract' to your water for the last watering.

You can use whatever extract you like but a word of warning is to stay away from anything that contains sugar as you will be asking for mould with sugar in the plant, extract is more of a flavour.

As the pots have been left to dry out the plants are waiting to get a good watering and will suck the extract all the way up to the top buds within 2 hours.

It is after 2 hours of the last watering you harvest, trim and hang. You will have to dry for longer and keep a close eye for mould as the bud will be heavy with water.

This is the risk you have to take why you want to infuse your plants with the extract. Enough air movement and a warm room will keep the danger of bud rot away. Always remember to dispose of any buds you find has bud rot. The mould is a spore which can do damage to humans if inhaled. Also move the mouldy buds out of the drying area as the spores can spread to other buds through the air.

You can also make the buds smell of something during the curing process in glass jars. Place cotton wool in with the buds and cover the cotton with the extract. the first way is the best of course.

So, I hope it goes well for you, just be extra careful during the drying process.

SL