The method of using v/s 1000ft/min & Mach 0.8 was used widely in my old company as the A320s we had always struggled to reach cruise levels. It was particularly used when having to make levels by Casablanca airspace when leaving the Northern Canary islands. The reason - the FMGS did a really poor job of maintaining speed (it chased it) and the aircraft made a good impression of a nodding dog. This technique would ensure you were level 10-20nm earlier than the managed mode would allow. It also kept a positive climb throughout. The alternative - enter the hold before entering Casa airspace.
There is no procedure in the FCOM to reflect this method but likewise there is nothing to say not. The risk is obvious but nothing that an attentive crew should worry too much about.