You can try Polo's SNEAKY program, or you can use the dnetc.exe -import filename.xxx feature.
to use the -import feature, Stop the client. Do a dnetc.exe -fetch of new blocks. rename the buff-in.rc5 file to buff-in1.rc5. repeat the -fetch and rename, incrementing the buff-inx.rc5 name until you have enough blocks in the multiple files. NOTE: Do not rename the last file. Then, use the dnetc.exe -import buff-in1.rc5 to import the new blocks back into the input buffer. Repeat for buff-in2.rc5, etc.....
But Sneaky is a lot easier to use. you can get the program
Here