Generating a SHA256 pkcs1v1.5 Blind RSA Signature using Chaum's Blind Signature Scheme
I can't believe it but I actually found an answer.
The following js code does exactly the padding scheme as detailed in the EMSA-PKCS1-v1.5 message encoding specification
function messageToEMSA_PKCS1_v1_5(message){
    // https://tools.ietf.org/html/rfc3447#section-9.2
    SHA256_DIGEST_INFO = &quot;30&quot; + &quot;31&quot; + &quot;30&quot; + &quot;0d&quot; + &quot;06&quot; + &quot;09&quot; + &quot;60&quot; + &quot;86&quot; + &quot;48&quot; + &quot;01&quot; + &quot;65&quot; + &quot;03&quot; + &quot;04&quot; + &quot;02&quot; + &quot;01&quot; + &quot;05&quot; + &quot;00&quot; + &quot;04&quot; + &quot;20&quot; ;
    T = SHA256_DIGEST_INFO + sha256(message);
    t_len = 51; // Just T.length 19 octets from the Digest Info + 32 octets from SHA-256

    ps_len = 256 - t_len - 3;
    PS = &quot;ff&quot;.repeat(ps_len);

    EM = &quot;00&quot; + &quot;01&quot; + PS + &quot;00&quot; + T;
    console.log(`EMSA-PKCS1-v1_5 encoded Message: ${EM}`);
    return EM;
}


Following this, the blind signature after being unblinded, would be a valid pkcs1v1.5 signature