Just ran into the same issue and posted it on irc today. atom came up with a great solution for this:
1) echo [[[[[ > pre.rule
2) hashcat <as usual> -j ^X^X^X^X^X -r pre.rule -r yournormalrule.rule
the -j ^X^X^X^X^X will prepend every password candidate from the dictionary with "XXXXX" making it long enough to pass the limit of 8 as the minimum length, the first "pre.rule" will then remove the "XXXXX" again. Finally your "normal" rules will be applied.
Worked for me.
1) echo [[[[[ > pre.rule
2) hashcat <as usual> -j ^X^X^X^X^X -r pre.rule -r yournormalrule.rule
the -j ^X^X^X^X^X will prepend every password candidate from the dictionary with "XXXXX" making it long enough to pass the limit of 8 as the minimum length, the first "pre.rule" will then remove the "XXXXX" again. Finally your "normal" rules will be applied.
Worked for me.