There actually is! Here is a guide I found for this method on a similiar distribution of Linux... hope it helps! All it does is mounts the iso as a cdrom and then you use a very basic slackware installer to point to that mounted "cdrom" and the install continues as normal......
1. getting the installer from ftp.slackware.com or other sites
1.1. Download install.zip.README and install.zip from the /slackware/slackware-current/rootdisks directory. Read the README mmediately to see if install.zip will work for you.
1.2. Download a kernel, a file named bzImage, from /slackware/slackware-current/kernels directory. The bare.i kernel works for most computers unless the computer uses scsi or some other hardware type.
1.3. From windows, unzip install.zip retaining the directory structure into a FAT partition. Copy bzImage into the unzipped /linux directory. Rename bzImage into vmlinuz. Still inside /linux, edit linux.bat so that only the reference to the FAT partition where /linux was placed is uncommented.
2. using the Slackware installer
2.1. Reboot into a DOS command prompt. Go to the drive where /linux is. Go into the /linux directory. Run linux.bat. Login.
2.2. Mount the slackware iso. For example, from the directory of the s/w iso do:
mount -t --ISO-NAME-HERE--.iso /mnt/cdrom -o loop
It is also assumed that you made a directory (for example /mnt/cdrom) for mounting the iso.
2.3 Run setup. Follow the steps. When you get to the point that you specify the source files, point to the /iso directory. For example /mnt/cdrom/iso. The selection of package directories will be displayed when you get it right -- /a /ap ... /kde ... /x /xap /y. /z would be missing. Just select everything and continue. Choose full installation. Go though the other steps until you are told to reboot.
I think this should work fine, although I haven't tried it myself... but hey, its worth a shot even if it doesn't work... Let me know if ya have success with this....