how can i backsig old keys with a smartcard system to solve the cross-certification workaround

[Jelle de Jong]

Werner Koch wrote:
> On Fri, 18 Jul 2008 11:03, jelledejong at powercraft.nl said:
> 
>> So my previous message and this message where properly signed? Then my
> 
> Yes:
> 
>   gpg: Signature made Fri Jul 18 11:00:05 2008 CEST using RSA key ID 6F63E479
>   gpg: WARNING: signing subkey 6F63E479 is not cross-certified
>   gpg: please see http://www.gnupg.org/faq/subkey-cross-certify.html for more information
>   gpg: please do a --check-trustdb
>   gpg: Good signature from "Jelle de Jong <jelledejong at powercraft.nl>"
> 
> However, I had to use 
> 
>   gpg --verify --no-require-cross-certification  
> 
> Thus I suggest that you do the backsig and upload the key again to the
> keyservers (best keys.gnupg.net)
> 

Thank you for taking the time to answer the message,

If you mean by "backsig" try to follow the instruction on the suggested 
subkey-cross-certify.html page then i tried to do this (see previous 
message)

I got the following error
gpg: secret key parts are not available

I tried searching the internet but found no solutions only this:
https://bugs.g10code.com/gnupg/issue673

The question now is, how can i backsig my old keys with my smartcard 
system to solve the cross-certification workaround?

Thanks in advance,

Jelle