Though not an oboist, (and not really having tried that hard to do "smears" and "doits" on my bassoon), I have adapted my clarinet playing to include these effects.
On clarinet it is mainly embouchre produced (unless you are doing the big glissando at the start of Rhapsody in Blue - which uses a combination of fingering and embouchre).
I get students to take a highish note using normal embouchre (in the range requiring the "eeeee" tongue / palate position - say around upper G on oboe).
From that note I get them to de-tune the note downwards mainly by modulating from "ee' to "eu" to "oo" to "aw". This drops the breath pressure and at the same time decreases the bite on the reed. The note then glisses downwards - it may take some perseverance to make the change as much as a semi-tone.
The next step is to try to start the same high note a semitone flat by starting with the "aw" jaw dropped low pressure setting of tongue & palate. Then reverse the modulation from "aw" through "oo", "eu" to "ee" increasing both bite and air pressure.
The next challenge is to do it on a range of notes and eventually in the course of playing. A little jazz knowledge will help identify the "blue" note and other suitable notes on which to smear.
Klezmer experts can really make the clarinet positively chuckle with these effects.
Christchurch New Zealand
Bassoonist / Teacher / Conductor