That’s a weird problem to have. The US has a huge bond market in part because the US has an absolutely enormous amount of debt, and the bonds are the US debt. The EU doesn’t have bloc-wide debt, for better or for worse.

As an interesting thought experiment, imagine a central bank associated with a debt-free country issuing bond-like instruments. They would set an interest rate (perhaps with no auction, because they have no actual obligation to sell a predetermined amount, although an auction could still be used), sell bonds, delete the money used to buy the bonds, and issue new money to repay them with interest when they mature. This could be used as a way to act efficiently as a reserve currency and to exert a degree of control over inflation and the economy, kind of like how the Fed does it. The bonds would likely be considered extremely secure on account of the issue being entirely debt-free.

I would be surprised if the EU did this as such, since the EU probably does not want to be in the business of competing for capital with its own members, who do have a fair amount of debt that they need to finance.