Well, you can put VERSION="..." in a hintfile, does this do what you need?
(it is a horrible hack, sometimes it will fail, but usually it will work perfectly
Example 1:
SBo's qtkeychain is 0.1.0
The latest qtkeychain is 0.3.0
=> put this in qtkeychain.hint, it will guess the download URL with sed
Example 2:
SBo's lyx package is 2.0.4
The latest lyx is 2.1.1, but the download URL can't be guessed automatically
=> put this in lyx.hint
Code:
VERSION="2.1.1"
DOWNLOAD="ftp://ftp.lyx.org/pub/lyx/stable/2.1.x/lyx-2.1.1.tar.xz"
In both examples, if you know the new md5sum then you can add MD5SUM=".....", or else it will ignore the md5sum.