I don’t claim credit for this idea just followed along the lines of this link:
I had to buy the 8mm makita collet from overseas on eBay ($18) as I couldn’t find a source here in the US. I could have bought one from Elaire but they were more expensive ($32).
Bought the ER11 extension from US vendor on eBay ($14) and a 13 piece collet set from US vendor on amazon ($21).
So for $53 I can now use any bit from 0.5mm to 7mm in the ER11 or an 8mm bit using the makita collet in the original chuck. The collets all have a 1/2mm range so any US size 1/16" to 1/4" will fit as well. Probably a 5/16" would work with the 8mm too.
Runout is still less than 0.001in using my cheapie dial indicator. Tool depth is about the same using 1/8" bits in the ER11 as it was using 1/4" bits in the original chuck.
I cut the ER11 extension down to fit the depth of the stock chuck using my lathe, but it could be done in a drill press with a hacksaw like the original description from inventables.