So in summary:
One cannot descend below 1000' above obstacles within 5nm, except to land/take off (rule 29), but:
One cannot descend below 1000' aal unless the actual weather is above the notified aerodrome operating minima (approach ban, article 49).
Where there is no notified aerodrome operating minima, one can calculate the AOM using the approved method (based on the Obstacle clearance height applicable to your aircraft type and the system minima) (para 7, article 49).
In other words the simple answer is one has to be visual at MSA to continue approach or shoot a published instrument approach. As far as I can see, a DIY approach is pretty much unfeasible to GA, unless of course one is referring to an approach with a 1000' MDH, which isn't really an approach, it is more a descent enroute.