One solution is to run a Knoppix CD and connect to the LTSP server via that. This has the advantage that laptops are more likely to have a CD-ROM drive than a floppy drive any more. It also leverages Knopppix's legendary hardware detection, meaning you have a better chance of having your wireless card being recognized. Using the Knoppix CD, boot to a command line by typing
at the boot prompt. Run netcardconfig to setup the wireless card, and then run the following command:
X -query 192.168.0.254
where 192.168.0.254 is the address of the LTSP server. This will direct an xdmcp query at the server, and you should get the same login screen as wired thin clients. You can even install Knoppix onto the laptop's hard drive, set it to boot to runlevel 3, get the wireless card all configured, and put the -X query command into a script so that it automatically runs upon bootup.
As I was writing this, I discovered that the Kubuntu 610 (Dapper) has a Remote Login option on its login screen. This, too, can be used to login as a client to the LTSP server. In both this and the Knoppix case, the local OS handles identifying the wireless card and loading the appropriate driver.