Rory
For what it is worth, the following is how I would approach things. First, I would look in the "Services of Boer War Officers" (Savannah publications) for your man and see if any periods of territorial-specific duty are shown. They sometimes are. If so, I would try and mesh those periods in with the bio's of Brig/Gen. Broadwood and Col. Pilcher. If that cannot be done, then generalities might have to be used. There are many references to both Broadwood and Pilcher in Amery, Maurice and Creswicke. For example, Creswicke Vol.7 [age xi) shows the components of Col. Pilcher's column in the Central ORC during Midsummer of 1901. Brig.Gen Broadwood's column on a later page is shown in the Northern ORC. There may well be more in other references.
ADC was an officer (at least a Captain) on the personal staff of a senior officer. Was your man an officer with the ASC? Again, "Services of Officers" should tell you one way or the other. It might be worthwhile to research out the structure of columns in the later period of the campaign. For example, did they routinely have an ASC detachment - or were they reliant for resupply from depots? If the latter, your man would have a fair bit of co-ordination to do. He was probably worked off his feet, anyway.
Anyway, that is the path I would follow. These are just suggestions.
Best regards
IL.