Most of today's online services (e.g., social networks, search engines, marketplace places) are centralized, which most users recognize as unsatisfactory for various reasons (e.g., centralized governance, censorship, loss of control over personal data). Blockchain technologies promise a new Web revolution (Web 3.0) through the decentralization of online services. However, one of the fundamental limitations for this revolution to happen at a planetary scale is the poor performance of today's permissionless blockchains. In this paper, we propose ALDER, a generic construction that multiplexes off-the-shelf permissionless blockchain protocols to address the performance bottleneck due to store-validate-forward block dissemination techniques in blockchain protocols. We apply ALDER to two representative blockchains, namely Algorand (Proof-of-Stake) and Bitcoin (Proof-of-Work), to illustrate the benefits it brings to blockchain performance. Our evaluations show that ALDER can drastically improve the throughput of blockchains when bottlenecks exist.