Marshal data to unmanaged memory and join them using IntPtr

Hi,

I have some bytes data that I am receiving in chunks. I want
to Marshal
this data to unmanaged memory chunk by chunk and join them
so that it
can be referenced by a single IntPtr.
For example, i receive 10 bytes and marshal it to unmanaged
memory and
point it using IntPtr_A. Then, when i receive other 7 bytes
of data, i
want to join it with last data on unmanaged memory so that
IntPtr_A can
now have total 17 bytes of data in continuation which can be
referenced
using IntPtr_A.

Is there any possible way to do that?

Thanks in anticipation...