We did a job earlier in the year for an avian charity. I emailed our man there to see if he had any ideas. See response below, not much help i'm afraid.
Sorry, Jackdaws are a nightmare and I don't know of any way of deterring them save extreme measures such as shooting which clearly I wouldn't condone. There may be some bird deterrent equipment such as spikes that may help but I couldn't vouch for their efficacy and the only thing you can do is periodically remove the build up of sticks (although you'd have to remove them/get rid of them/burn them to ensure they weren't available, as they'll continue to collect until they miss the breeding window). Clearly this is not always practicable for roof-mounted systems
There's probably some money to be made if you can find a reliable deterrent measure. It's a bugger, but there it is.