Christoph
Our Radar Dome is mounted in nearly the same spot and we use the staysail and it tacks around the dome. We do have the Kato radar mount. Have you tried to move the staysail around the dome simply while at the docks with little winds? I bet it will work just fine.
One thing to recognize is that these small staysails are really used very little. They are mostly used...
#1. To look cool and look very salty under a full sail three sail rig giving the boat maybe 0.5 knot increase.
#2. To motor into strong winds 10-15 degrees off the bow.
#3. To run off the wind in a storm at sea in 30-40+ knots.
#4. To simply have out in jib tacking situations to help the jib go around the staysail forestay.
So, the reality of tacking the staysail is actually very low, matter of fact, I hardly ever use the staysail and I only use in the above 4 situations. With this reality, I personally would not worry about this too much. Simply roll out the staysail on the tack you want when you want to use it and that will be 1 time out of 20 times you go sailing.
Back in 2002 when we added our radar, I documented the work here:
fhayden.com/rockhallfleet/islandspirit/radar.htm
Here is one photo showing our install.
I hope this helps.
Hayden