The use of broadcasting (126.90) can be found on Africa Jeppesen Manual 1. The broadcasting includes almost all Africa. You have references about this on the enroute charts as well.
Concerning the 2 Nm offset looK for NOTAM SBAO FIR 2004120E733V01 N0036/04
Basically it says:
STRATEGIC LATERAL OFFSETS IN OCEANIC AIRSPACE TO MITIGATE COLLISION RISK AND WAKE TURBULENCE :
PILOTS SHOULD USE THE STRATEGICAL LATERAL OFFSET PROCEDURE AS STANDARD OPERATING PRACTICE IN THE COURSE OF NORMAL OPERATIONS TO MITIGATE COLLISION RISK AND WAKE TURBULENCE.THE STRATEGIC LATERAL OFFSET PROCEDURE WILL BE IN FORCE IN THE ATLANTICO FIR , DAKAR , OCEANIC FIR , CANARIAS , SAL OCEANIC FIR.
- STRATEGIC LATERAL OFFSETS SHALL BE APPLIED ONLY BY AIRCRAFT WITH AUTOMATIC OFFSET TRACKING CAPABILITY
-THERE ARE THREE POSITIONS THAT AN AIRCRAFT MAY FLY : CENTERLINE , 1 OR 2 NM OFFSET RIGHT OF CENTERLINE.
-THERE IS NO ATC CLEARANCE REQUIRED FOR THIS PROCEDURE AND IT IS NOT NECESSARY THAT ATC BE ADVISED .REF
NR 3.5-8 , AIP BRAZIL