I've decided to use grease but that's what I'm thinking, make some adapters. Quite a lot of the large motors I've worked on had extension tubes for the grease nipples because they would have been inaccessible otherwise. It's a daft design on their part I think, if only they were 6mm instead of 4mm. I'm thinking about a right angle adapter made of brass with a 4mm male thread and a 6mm female to take a standard nipple.