Azure AD B2C Custom Policy SignUp only with loyaltynumber and email pre-filled - azure-ad-b2c

Question

I'm creating a custom Sign up only policy that should receive two attributes in the url:
email adress (optional)
loyaltynumber (required)
If I have the email address in the url I want it to be pre-filled in the box (and read-only, but I could fix that with html/css?) and the loyalty number.
I've allready created the custom policy but I cannot get the email (=username) pre-filled.
I've created a UserJourney:
<UserJourney Id="SignUp">
<OrchestrationSteps>
<OrchestrationStep Order="1" Type="ClaimsProviderSelection" ContentDefinitionReferenceId="api.idpselections.signup">
<ClaimsProviderSelections>
<ClaimsProviderSelection TargetClaimsExchangeId="SignUpWithLogonEmailExchange" />
</ClaimsProviderSelections>
</OrchestrationStep>
<OrchestrationStep Order="2" Type="ClaimsExchange">
<Preconditions>
<Precondition Type="ClaimsExist" ExecuteActionsIf="true">
<Value>objectId</Value>
<Action>SkipThisOrchestrationStep</Action>
</Precondition>
</Preconditions>
<ClaimsExchanges>
<ClaimsExchange Id="SignUpWithLogonEmailExchange" TechnicalProfileReferenceId="LocalAccountSignUpWithLogonEmail" />
</ClaimsExchanges>
</OrchestrationStep>
<!-- This step reads any user attributes that we may not have received when in the token. -->
<OrchestrationStep Order="3" Type="ClaimsExchange">
<ClaimsExchanges>
<ClaimsExchange Id="AADUserReadWithObjectId" TechnicalProfileReferenceId="AAD-UserReadUsingObjectId" />
</ClaimsExchanges>
</OrchestrationStep>
<OrchestrationStep Order="4" Type="SendClaims" CpimIssuerTechnicalProfileReferenceId="JwtIssuer" />
</OrchestrationSteps>
</UserJourney>
And a Signup policy:
<BasePolicy>
<TenantId>tenant.onmicrosoft.com</TenantId>
<PolicyId>B2C_1A_TrustFrameworkExtensions</PolicyId>
</BasePolicy>
<ClaimsProviders>
<ClaimsProvider>
<DisplayName>Local Account</DisplayName>
<TechnicalProfiles>
<TechnicalProfile Id="SelfAsserted-LocalAccountSignin-Email">
<InputClaims>
<!-- Add the login hint value to the sign-in names claim type -->
<InputClaim ClaimTypeReferenceId="signInName" DefaultValue="{OIDC:LoginHint}" />
</InputClaims>
</TechnicalProfile>
</TechnicalProfiles>
</ClaimsProvider>
</ClaimsProviders>
<RelyingParty>
<DefaultUserJourney ReferenceId="SignUp" />
<TechnicalProfile Id="PolicyProfile">
<DisplayName>PolicyProfile</DisplayName>
<Protocol Name="OpenIdConnect" />
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="displayName" />
<OutputClaim ClaimTypeReferenceId="givenName" />
<OutputClaim ClaimTypeReferenceId="surname" />
<OutputClaim ClaimTypeReferenceId="email" />
<OutputClaim ClaimTypeReferenceId="objectId" PartnerClaimType="sub"/>
<OutputClaim ClaimTypeReferenceId="tenantId" AlwaysUseDefaultValue="true" DefaultValue="{Policy:TenantObjectId}" />
</OutputClaims>
<SubjectNamingInfo ClaimType="sub" />
</TechnicalProfile>
</RelyingParty>
</TrustFrameworkPolicy>