It would be helpful if you supplied the library you were using to work on excel files, but here's a buckshot of solutions, based on some assumptions I'm making:

• Based on the first paragraph in the io module's documentation, it sounds like all the concrete classes- including BytesIO- are file-like objects. Without knowing what code you've tried so far, I don't know if you have tried passing the BytesIO to the module you're using.
• On the off chance that doesn't work, you can simply convert BytesIO to a another io Writer/Reader/Wrapper by passing it to the constructor. Example:

.

import io

b = io.BytesIO(b"Hello World") ## Some random BytesIO Object
print(type(b))                 ## For sanity's sake
with open("test.xlsx") as f: ## Excel File
    print(type(f))           ## Open file is TextIOWrapper
    bw=io.TextIOWrapper(b)   ## Conversion to TextIOWrapper
    print(type(bw))          ## Just to confirm 

• You may need to check which kind of Reader/Writer/Wrapper is expected by the module you're using to convert the BytesIO to the correct one
• I believe I have heard that (for memory reasons, due to extremely large excel files) excel modules do not load the entire file. If this ends up meaning that what you need is a physical file on the disk, then you can easily write the Excel file temporarily and just delete it when you're done. Example:

.

import io
import os

with open("test.xlsx",'rb') as f:
    g=io.BytesIO(f.read())   ## Getting an Excel File represented as a BytesIO Object
temporarylocation="testout.xlsx"
with open(temporarylocation,'wb') as out: ## Open temporary file as bytes
    out.write(g.read())                ## Read bytes into file

## Do stuff with module/file
os.remove(temporarylocation) ## Delete file when done

I'll hope that one of these points will solve your problem.

How about we write and read gzip content in the same context like this?

#!/usr/bin/env python

from io import BytesIO
import gzip

content = b"does it work"

# write bytes to zip file in memory
gzipped_content = None
with BytesIO() as myio:
    with gzip.GzipFile(fileobj=myio, mode='wb') as g:
        g.write(content)
    gzipped_content = myio.getvalue()

print(gzipped_content)
print(content == gzip.decompress(gzipped_content))

Since Python 3.2 it's possible to use the BytesIO.getbuffer() method as follows:

from io import BytesIO
buf = BytesIO(b'test')
with open('path/to/file', 'wb') as f:
    f.write(buf.getbuffer())

This way it doesn't copy the buffer's content, streaming it straight to the open file.

Note: The StringIO buffer doesn't support the getbuffer() protocol (as of Python 3.9).

Before streaming the BytesIO buffer to file, you might want to set its position to the beginning:

buf.seek(0)

this is a memory stream but still a stream. The position is stored, so like any other stream if you try to read after having written, you have to re-position:

import io
in_memory = io.BytesIO(b'hello')
in_memory.seek(0,2)   # seek to end, else we overwrite
in_memory.write(b' world')
in_memory.seek(0)    # seek to start
print( in_memory.read() )

prints:

b'hello world'

while in_memory.getvalue() doesn't need the final seek(0) as it returns the contents of the stream from position 0.