Throwing a loop of numbers on the end seems far more feasible. I put together a hasty Python implementation which can immediately find three hits at 5 characters. TQDM is reporting ~450k tries per second, so depending on how lucky you are, would probably want to redo in a faster language to solve for 7+

    import hashlib
    import itertools
    
    import tqdm
    
    BLOCKS_SIZE = 5
    sentence_prefix = "The SHA256 for this sentence begins with:"
    
    itos = {0x00:"zero", 0x01:"one", 0x02:"two", 0x03:"three", 0x04:"four", 0x05:"five", 0x06:"six", 0x07:"seven", 0x08:"eight", 0x09:"nine",
           0x0a:"a", 0x0b:"b", 0x0c:"c", 0x0d:"d", 0x0e:"e", 0x0f:"f"}
    for nums in tqdm.tqdm(itertools.product(itos.keys(), repeat=BLOCKS_SIZE)):
        sentence = f"{sentence_prefix} {', '.join(itos[num] for num in nums[:-1])}, and {itos[nums[-1]]}."
        hash_true = hashlib.sha256(bytes(sentence, "utf8")).hexdigest()
        guessed_prefix = "".join(f"{n:x}" for n in nums)
        true_prefix = hash_true[:BLOCKS_SIZE]
        if guessed_prefix == true_prefix:
            print("collision")
            print(sentence)
            print(hash_true)