Usually for the 'dreaded c' (constipation), we suggest increasing water intake and exercise, use some of the orange flavored sugar-free Metamucil 9mix it and drink it right down before it gets thick and gloppy - argh!), some people have had good results with psyllium.
I resorted to a stool softener once in a while called Surfak - I used 2 a day to get things going, then 1 a day; I found that when I ate broccoli and oatmeal frequently, i could cut out the Surfak.
Some of my co-losers used Colace.
Yes, up to 1 tablespoon of canola or olive oil is also listed as an option but remember, oils are very high in calories. 1 teaspoon of most oil varieties has 45 calories, 1 tablespoon is over a 100.
Personally, I'd suggest that you try the other options first. I would definitely read the label before I slurped up any Ranch Dressing - oil of course has no carbs; many Ranch dressings contain carbs, calories and fat unless it is Walden Farms or some other diet dressing and then that defeats your purpose for wanting to use olive or canola oil as a blasting cap!
You may want to read some of my previous posts about constipation by using the search feature.
Constipation is
NO fun, I feel for ya!