Every single customer that comes to me wanting to print with metallic or white inks on a solvent printer I tell them you don't want to do it and most of the time they are convinced. Every once in a while we get a customer who says they must have it. As soon as the machine is installed we have an office bet on how soon they will call asking to convert to CMYKx2. Not one machine we have setup with metallic has stayed that way for more then 2 years.
Anyway, technically you could run a cleaning cartridge in place of the metallic ink. The easiest way would be to get a permanent metalic ink chip and install it on a cleaning cartridge. I would only use OEM cleaner which is more expensive but you can sleep at night knowing it was meant to be run though the machine.
Disclaimer: First, Roland does not recommend this setup so if you have any type of warranty on the machine or heads, make sure you are willing to lose that. Second, every time you want to use the metallic you will have to either manually refill the lines, which takes a good amount of time and can be messy. Or you will have to have the machine refill the line in which case you will waste a good amount of ink. So if you still save money after that, it's still a good idea. Third, there is some evidence, but it is not conclusive, that running cleaning solution through the head instead of ink can wear it out faster. I don't know if there is any truth to that but I can see running a much less viscous solution through could affect the head in some way over the long term.
At the end of the day I would recommend converting to CMYKx2 instead if you want to really save time and money. Then just print on metallic vinyl when you need the effect or outsource it.
