An internet trawl suggests an outfit called WTS Travel in Singapore will be running coaches from the Singapore Flyer at 9.30am straight to the park, and back in the evening.

Yes, you'll have to go through customs & immigration in both directions and on both sides.

If you wanted to do it yourself you could hop across to Johor Baru on the service bus then get a taxi from there, or go to the Malaysia taxi terminal in Singapore (nr Bugis) and they can take you to the Johor area. (Not sure how you get back, though...)