Help with Robinhood’s margin spending feature

Hi all,
So I decided to move all of my uninvested cash into Robinhood to take advantage of their 4.15% interest rate with Robinhood Gold. I did the math, and if you have about 2400 or more in cash, it's worth it to pay the 5 dollar fee for Gold, as you will make it back in interest every month and then some. So now that I have free Robinhood Gold, I got to looking at the other benefits and I saw free margin usage up to 1000 dollars.

I'm wondering if there is a way to earn the 4.15% interest on my borrowed 1000 dollars. Or, using the spending feature, where you are allowed to withdraw money out of Robinhood on margin, I'm wondering if I could withdraw my 1000 dollars and invest in an I bond or some other type of bond for an even better interest rate.

However, I can't seem to figure out how to get it to say I'm using margin without actually purchasing so much stock that I need to use margin. In other words, is there a way to borrow on margin while having cash in your account? Or is that not how margin works?

Thanks in advance