Under the proposals, up to 300,000 Conservative supporters would rank the party's Holyrood List candidates, along with 11,000 members.
An internal consultation has stated the plan would "widely enhance" the recognition of potential MSPs.
In common with other parties, the franchise for Tory selections is restricted to card-carrying members.
However, the party last year announced a review of the system for ranking so-called regional List candidates.
At present, 12 of the party's 15 MSPs were elected this way.
A consultation paper, which asks for submissions to be sent to deputy leader Jackson Carlaw, has proposed far-reaching changes to the status quo.
The document proposes that members will continue to determine who can stand as first-past-the-post and regional List candidates.
However, a new tier of non-members who have 'pledged' support to the party will be able to rank List candidates in order of preference.
It notes: "In excess of 300,000 people will be invited to participate rather than the current membership of some 11,000+."
At the last Holyrood election, the Tories won 245,967 votes on the List.
The consultation explained the perceived benefits of the plan: "It will widely enhance the recognition of the Conservative list of regional candidates beyond the locally promoted, first past the post candidate, and is intended to enhance second vote commitment."
It added: "Scottish Conservatives will establish the greatest democratisation of the regional list ranking process of any political party in Scotland."
Although the document accepts that an increased selectorate could include SNP and Labour supporters, it argues that these anomalies will not be "sufficient to prejudice any outcome". Carlaw's plan concedes the radical reform will be "expensive" and notes an appeal procedure will accompany any ballot.
A number of initiatives have been ruled out for the time being, including telephone canvassing of those voting in the selections and term limits for MSPs.
Fully 'open' primaries, where all voters select candidates, rather than just party supporters, have been rejected.
The consultation also invites opinions on how the new "pledgers" could be balloted, with options including a postal vote or a special hustings.
If introduced, the Tories would be the first party north of the border to use a primary to select their candidates.
The Scottish party's big hitters - leader Ruth Davidson, Carlaw and Murdo Fraser MSP - are all List members.
A Tory source said: "Open primaries would have been better, but this is a step in the right direction."
A Scottish Conservative spokesman said: "We are consulting widely on this proposal, which if accepted, would be the biggest extension of democratisation of the list ranking process by any political party in Scotland today. Our members will make the final decision."
An SNP spokesperson said: "This move looks like part of the simmering row within the Tory Party about the record of their list MSPs since 1999, and a panicked reaction to their dwindling membership numbers in Scotland."