[puckedoff]

^ Couple DIY options, not really the solution you asked for but food for thought -

1 - You can just put the $500 into one of those each month, and then rotate through each ETF.

2 - Depending on who you bank with, they may have a fund that is free to trade in and out of (watch for cash out fees, minimum holding periods) that you could split your allocation like in above and then just transfer to the matching ETF when it is a more sizeable amount.
Edit to add info: TD has 'E-series' funds which have no purchase cost, and very low MER (for S&P Index E-series, it is 0.35%). I can contribute my $500 to this each month, and then when I have $5000 I can transfer it to an S&P 500 ETF so that my trading fee on that ETF does not eat up all my principal)