Went yesterday.
The route out was canal, coming off (up steps) at Clifton Hall Road, then approaching Jupiter from the west on the B7015 (which is not a particularly quiet or slow B-road, we took the pavement which is quite ridable, surfaced in fine gravel).
There's 5 cycle racks which are an unusual design with hoops hanging down from a supporting frame, not brilliant but they work.
There's no mention of cycling in either their leaflet or on the website.
On the way home went east out the entrance, along the pavement on A71, crossing before Linburn to head up the back road towards Kirkliston, under the railway and then the Long Dalmahoy Road, through Heriot Watt etc.
Back to Jupiter, annoyingly, the east gate into the estate is a big, automatic thing that you need a code for, so you can't access it from this side, which would allow you to cut off any requirement for being on the A roads or circuitous detours to approach from the west if you were coming from canal / Edinburgh. A small side gate for foot/cyclists would be very welcome.
The art itself is excellent, thoroughly enjoyable place. Good café too, although rather pricey (£18 for 2 coffees and 2 sandwiches, then £17 for 2 adults). It ain't a cheap day out. I suppose you could bring your own lunch but picnics are not welcome.