How to start Azure B2C User Flows from Blazor WASM application using MSAL 2

I've successfully configured the Azure B2C service so that a Blazor WASM application will launch my B2C_1_Signin User Flow by navigating to /authentication/login in my application.

Now, I'm trying to launch my B2C_1_Signup User Flow. When I try /authentication/register, I get a message saying that Registration is not supported. I assume I am missing some configuration, but I can't find any documentation on how to proceed.

Here's what I've tried:

1. In my wwwroot/appsettings.json, I've tried adding settings to tell MSAL what User Flows to use:

{
  "AzureAdB2C": {
    "Authority": "https://xxx/yyy/B2C_1_Signin",
    "ClientId": "0000-0000-0000",
    "ValidateAuthority": false,
    "SignUpPolicyId": "B2C_1_Signup",
    "SignInPolicyId": "B2C_1_Signin"
  }
}

...but this doesn't work.

2. I crawled through the Microsoft.AspNetCore.Components.WebAssembly.Authentication source code until I found the Registration is not supported message. Based on the surrounding code, it looks like it is expecting a value in RemoteRegisterPath, so I modified my Program.cs as follows:

builder.Services.AddMsalAuthentication(options =>
{
    builder.Configuration.Bind("AzureAdB2C", options.ProviderOptions.Authentication);
    options.ProviderOptions.DefaultAccessTokenScopes.Add("openid");
    options.ProviderOptions.DefaultAccessTokenScopes.Add("offline_access");
    options.ProviderOptions.LoginMode = "redirect";

    options.AuthenticationPaths.RemoteRegisterPath = "https://xxx/yyy/B2C_1_Signup";
});

Doing this launches the User Flow, but it seems to need the full URL from the Azure B2C site:

https://xxx/yyy/oauth2/v2.0/authorize?p=B2C_1_Signup&client_id=0000-0000-0000&nonce=defaultNonce&redirect_uri=https%3A%2F%2Flocalhost%3A5001%2Fauthentication%2Flogin-callback&scope=openid&response_type=code&prompt=login&code_challenge_method=S256&code_challenge=F1ut2KaRX...

Since I don't want to handle the full PKCE exchange (e.g. - create the code_challenge and handle the returned code), I'm wondering how to proceed.