This may be a lil messy, but be as clean and neat as possible so it's not noticable...
you will need about 3 or 4 of those cheap lighters (the ones you can adjust the flame) - Dollar Store FTW!
gently dig your way down to the roots, try and find a few of the bigger ones (small ones may be a lil mor difficult) choose 2 or 3 of them, and give a tiny lil snip (razor will work best) now take your lighters, and for each root you snipped, unscrew the lighter ALL the way (the fluid will shoot out so make sure you aim it at the root) it will not only shoot fluid into the root, but will also freeze it

now cover it back up and fix the soil so it looks like it was touch
afterwards, you can also try unscrewing a lighter and dropping it in a cup of water (diluted lighter fluid? :P ) then water the plants with that...
NOTE: make sure you have either an open window or a fan and some car airfresheners jus incase

IF there is any smell, it should be gone in 30 mins or so...
Lemme know if it works (h)