Don't know of a way to enter frequency by the remote, but download this file for the 3805 which contains the codes for A to E and 1 to 8 and then program your remote with a small delay between (for example) A and 1. I suspect the codes are the same.

[Link: remotecentral.com]

Or you could use the pdf file in the above in conjunction with DenonHexGen to create the codes you need.

[Link: remotecentral.com]